The Clockwork Rocket

“How can it have escaped?” Giulio asked. “Are you saying it’s already reached a height where gravity’s negligible?”

His tone of incredulity was appropriate, but he’d missed the point. Nereo said, “At the altitude it had reached on my last observation, gravity is barely diminished—but it was already moving rapidly enough to guarantee that it would never be brought to a halt. Not by the world—though the sun still had hold of it.”

Yalda looked to Amando, and together they managed to slide the tinted pane aside without the pieces falling on them. The bunker’s five occupants climbed to their feet and scrambled up onto the sand, slipping between the ground and the mirror.

Yalda searched the sky, high to the east. There weren’t many Hurtlers today to confuse the view, and she could see a faint gray speck that could only be Eusebio’s house-sized pillar of rock—engines still blazing, still gaining speed. The escape velocity for the sun itself was only three times greater than the world’s. Given the results from earlier yield experiments, if the rocket burned all its fuel without mishap it could actually end up leaving the solar system.

Giulio addressed Eusebio. “You should come to Red Towers and talk about your plans. Nereo’s already given public lectures on rotational physics, so the ideas aren’t completely new to people, but I can run some articles in the Report beforehand to help your audiences prepare.”

Yalda wondered what was in the crops around Red Towers that was missing from Zeugma’s diet.

Eusebio said, “I’d be delighted.”

Yalda thanked Nereo for his participation. “It’s a pleasure,” he said. “I don’t know if your guess about the Hurtlers is right, but I’m glad someone’s thinking about these possibilities.”

“I can’t interest you in a place on the rocket?”

Nereo buzzed with mirth. “I’d rather stay safe on the ground, and wait for your dozen-fold-great-grandchildren to tell me all the marvelous science they’ve discovered.”

Yalda said, “I get that answer a lot.”

She wished she could have spent longer with Nereo, but he and Giulio needed to get back to Red Towers. Amando brought one of the trucks out of the shed and sped off across the desert with their guests.

Eusebio turned to Yalda. “Will you come to Red Towers with me? Tour the show?”

“If I can get leave from the university.” Yalda hesitated. “Do you think you could pay me a small fee for that?”

“Of course.” Eusebio had invited her several times to become an employee, but so far she’d resisted; she’d wanted to retain her independence, in order to be able to speak her mind to him freely.

She added apologetically, “If I’m not teaching I won’t get paid, and it’s not fair on Lidia and Daria to be looking after the children with no help.”

“Hmm.” Eusebio had already made it clear that he disapproved of what the three of them were doing: women—however capable they could be in other spheres—had not been shaped by nature for the raising of children. There were plenty of widowers in Zeugma desperate for heirs, and prepared to treat them like the flesh of their own co.

But he had more important things to think about than the flaws in Yalda’s domestic life. “Beyond spreading the news to the citizenry of Red Towers,” he said, “I’m hoping your colleague Nereo can arrange a meeting for me with his patron.”

“You can’t get an introduction to Paolo yourself?” Yalda was amused. “Whatever happened to the plutocrats’ network?”

“Networks, plural. They’re not all joined together.”

“Why do you want to meet Paolo?”

“Money,” Eusebio replied bluntly. “My father’s set a ceiling on my investment in the rocket. If I’m going to have to build the whole structure myself—mining and transporting all the sunstone, incorporating it into an artificial shell… if I tried to match the scale of Mount Peerless the costs would be greater by a factor of several gross, but even the smallest viable alternative is far beyond what I can afford on my own.”

“Have you thought of bribing all the people who are entitled to vote on the observatory?” Yalda suggested. “Not just with a shiny new telescope—with money they can put in their own pockets?”

Eusebio was insulted. “I’m not a fool; that was my very first plan. But Acilio has the Council scrutinizing the University’s business very closely, and he has so many spies in the University himself that I doubt I could get away with that kind of thing.”

Yalda joked, “I’m always willing to kill Ludovico, for a nominal fee.”

Eusebio regarded her with a neutral expression for an uncomfortably long moment.

“Don’t tempt me,” he said.

As the train approached Red Towers, Yalda was surprised to discover that the city still lived up to its name. She’d read that the local calmstone deposit with the eponymous hue had been mined out long ago, but now she could see with her own eyes that the skyline still bore an unmistakable red tint. Perhaps the original buildings had been lovingly preserved. Either that, or they’d all been recycled as decorative veneer.

Nereo met her at the station—along with all four of his children, who fought with each other for the thrill of carrying her luggage. Seeing how young they were, Yalda guessed that his co must have lived almost as long as her own grandfather. Nereo was still healthy, though—and no doubt he’d made arrangements for the children to be cared for even if some tragedy struck him down.

“Your friend Eusebio’s already at the house,” Nereo said.

“He had some business in Shattered Hill,” Yalda explained. “We’ve come in from opposite directions.”

Nereo lived within his patron’s walled compound. Yalda’s skin crawled as they walked past the sentries with their knife belts, but the children took the sight for granted. “It’s just a tradition,” Nereo told her, noticing her discomfort. “Paolo has no enemies; those weapons have never been used.”

“Don’t the guards get bored, then?”

Nereo said, “There are worse jobs.”

Eusebio was sitting on the floor in the guest room, reading a copy of The Red Towers Report. He greeted Yalda, then added in a tone of disbelief, “This man Giulio actually read and understood every word in the briefings I sent him. He raises some objections and concerns, but… they’re all entirely sensible.”

“Let’s just strap the whole city to a rocket and get it over with,” Yalda suggested. “Let Red Towers flourish in splendid isolation in the void for an age or two, then they can come back and teach the world how to live.”

They only had a couple of bells before the show, so they went to the hall to familiarise themselves with the layout. Yalda hadn’t been able to bring the equipment to produce the projected backdrops they’d used in Zeugma, but Giulio had organized printed sheets bearing the same material, which would be handed to the audience as they entered. That meant keeping the general lighting on during the performance.

“Seeing all those faces is going to make me anxious,” she told Eusebio, standing on the stage at the front of the empty hall.

“Don’t worry, you’re a professional now.” He squeezed her shoulder reassuringly.

The solution only came to her when she finally stepped out in front of the crowd: she delivered exactly the same message as in Zeugma, but she shifted her attention to her rear gaze and focused on the blank wall behind her, allowing herself to imagine that all the people in the hall were staring, not at her, but at the same soothing whiteness.

After Eusebio had done his part—with a few changes from the original version in which he’d boasted of a rocket the size of a mountain—it was time for questions. Everyone they’d spoken to in Red Towers had told them that they’d have to take questions from the floor; it was the custom here, and if they defied it they would not be forgiven. Giulio—whose employers had paid half the cost of renting the hall, in exchange for the right to display the paper’s name prominently throughout the venue—joined Yalda and Eusebio on stage to moderate.

Yalda braced herself for the predictable “Why can’t I walk to yesterday?” jokes, or perhaps even the perennial “Where’s your co?”

The first questioner Giulio selected, an elderly man, called out, “How will you keep the machinery repaired?”

Eusebio said, “There’ll be workshops within the rocket, equipped for every eventuality.”

The man was unimpressed. “And factories? Mines? Forests?”

“There’ll be stocks of minerals,” Eusebio said, “and gardens for raw materials as well as for food.”

“Stocks to last an age? Soil to last an age? All inside one tower? I don’t think so.”

Giulio chose another questioner.

“How will you control the population?” the woman asked.

“At the moment we have more of a shortage of travelers than an excess,” Eusebio replied.

“Double that number a few dozen times,” she suggested, “then tell me where you’ll put them, and how you’ll feed them.”

Eusebio was beginning to look flustered. Yalda said, “There’ll be the same mortality rates on the rocket as we experience anywhere else. No city’s population actually doubles in a generation.”

“So there’ll be no progress in medicine, then? For era after era, the only thing these travelers will care about is dealing with the Hurtlers… which no longer even threaten them?”

Yalda said, “Progress in medicine could end up controlling population growth as much as it lowers mortality.”

“Could—but what if it doesn’t?”

The questions continued in this fashion: tough but undeniably pertinent. It felt like an eternity before Giulio called a halt; Yalda was so exhausted that it took her a moment to realize that the audience was now cheering enthusiastically.

“That went well,” Giulio whispered to her.

“Really?”

“They took you seriously,” he said. “What more did you want?”

In the foyer, they recruited more than three dozen ground crew volunteers, but no passengers. People here were far more willing than their cousins in Zeugma to accept Yalda’s premise about the Hurtlers, and even the abstract principle behind Eusebio’s solution—but no one was confident that he could build the kind of habitation in which they’d want their own grandchildren to spend their entire lives.

The servant ushered Yalda, Nereo and Eusebio into the dining room, then withdrew.

Paolo was standing at the far end of the room, flipping through a thick stack of papers. He looked younger than Yalda had expected, perhaps a bit more than two dozen years old. He put the papers down on a shelf and approached, gesturing at a wide circle of cushions on the floor. “Welcome to my home! Sit, please!”

Nereo introduced Yalda and Eusebio. Yalda tried not to be intimidated by the opulence of the room; the walls were decorated with an abstract mosaic, and there was a bewildering array of food spread out in front of them, almost none of it familiar to her. To her eye, there was enough to feed at least a dozen people—and when six young men entered the room, the quantity began to seem almost reasonable—but it turned out that Paolo’s sons were just passing through to greet his guests, and would not be joining them.

Six sons! Had he adopted some of them, or taken two co-steads? Either way, if it was a family tradition the house would be overflowing with grandchildren.

The formalities over, Paolo sat with them and urged them to start eating. Yalda made a conscious decision not to hesitate—not to stare at the dishes and try to guess their origins. She was confident that nothing here would be too repellent, let alone dangerous, so it didn’t really matter that she had no idea what she was putting in her mouth. The first few flavors were strange, but not unpleasant. She decided to adopt a fixed expression of mild enjoyment and maintain it throughout the meal, regardless.

Paolo addressed Eusebio. “I’ve heard about your rockets; an extraordinary venture.”

“It’s only just beginning,” Eusebio replied. “To send people safely into the void will take many more years of work.”

“I admire the audacity of your vision,” Paolo said, “and I appreciate that the Hurtlers might well become dangerous. But what exactly do you think your travelers will bring back from a trip into empty space?”

“That’s difficult to predict,” Eusebio admitted. “Imagine, though, how wondrous our cities would appear to a visitor from the eleventh age. They had no engines, no trucks, no trains. Only the crudest lenses. No reliable clocks.”

“But what comes next?” Paolo wondered. “An engine that runs a little more smoothly? A clock that loses no time in a year? Undoubtedly civilized refinements, but how would they safeguard us against the Hurtlers?”

Eusebio said, “Have you heard of the Eternal Flame?”

Yalda was glad she’d already committed to a policy of benign inexpressiveness.

Paolo buzzed amiably—not mocking his guest, but treating this invocation as if it could only have been meant as deliberate, flippant hyperbole.

Eusebio’s tone remained scrupulously polite, but Yalda could see him struggling to keep his frustration in check. “The old stories of the Eternal Flame were misguided in their details,” he said, “but modern ideas suggest that such a process might actually be possible.” He turned to Nereo. “Am I wrong about that?”

Nereo said cautiously, “Rotational physics doesn’t rule it out immediately, the way our earlier understanding of energy did.”

Paolo was surprised. “Honestly?” He put down the loaf he’d been chewing. “So all those wild-eyed alchemists might simply have given up too soon? Ha!” He shot Nereo a reproving glance, as if his science adviser might have thought to mention such an interesting fact a few years earlier.

Eusebio said, “Sir, may I tell you one message we received very clearly from the people of Red Towers last night?”

“Certainly,” Paolo replied.

“My venture, as it stands, is too modest,” Eusebio confessed. “Nobody believes that a few dozen people in a vehicle perhaps the size of this compound could survive long enough to reap the benefits of their situation. The basic physics of the trajectory puts no limit on the length of their journey—no limit on the advantage they could have over us in years. But the practicalities of their situation will be the determining factor. A robust society requires a certain scale, in both people and resources. An isolated camp in the desert with well-chosen supplies might endure for a generation or two, but it takes a whole city to flourish for an age.”

Paolo said, “I understand.” He was silent for a while. “But how large a rocket would be large enough? No one knows. It’s a very big risk to take, based on nothing but guesswork.”

“If it stops the Hurtlers from destroying us,” Eusebio replied, “how could it not be worth it?”

“But that judgment depends not only on the travelers succeeding,” Paolo reasoned, “but also on an absence of other solutions. The same resources spent here on the ground might solve the problem more efficiently. I can’t speak for others, but I do like having my own money doing its work somewhere nearby, where I can watch over it.”

“Yes, sir.” Eusebio lowered his gaze. The rejection could not have been clearer.

Paolo turned to Nereo. “So, perhaps the Eternal Flame could be made real?”

“Perhaps,” Nereo conceded reluctantly. “But there are a number of subtleties to be considered, some of which we barely understand.”

“What if I hired a gross of chemists to go out into the desert and start testing every possible combination of ingredients? Somewhere far from any people they could harm?” Nereo didn’t reply immediately, but Paolo was already warming to his own vision. “We could require that each experiment take place at a location on the map that encoded the particular choice of reagents. That way, it would be apparent from the positions of the craters which reactions should never be attempted again.”

“Ingenious, sir,” Nereo declared. He was being sarcastic, but Paolo chose to take him at his word.

“The credit,” Paolo replied, “should go to our guest, who delivered this inspiration to me.” He bowed his head toward Eusebio.

Throughout their second, final show in Red Towers, Eusebio kept up an admirably professional veneer of optimism, but as soon as they were back in Nereo’s guest room he slumped against the wall.

“It’s too much,” he said numbly. “I can’t do this anymore.”

“We can find someone else to take over the recruitment drive,” Yalda suggested.

“I’m not talking about the recruitment drive! The whole project is impossible. I should give up this idiocy and go back to the railways; let someone else worry about the Hurtlers. I’ll probably be dead before the worst of it, anyway. Why should I care?”

Yalda walked over to him and touched his shoulder reassuringly. “So Paolo won’t invest in the rocket. He’s not the only wealthy person on the planet.”

“But Red Towers is as good as it gets,” Eusebio said. “Journalists here understand the whole message. People listen to our plan and offer intelligent, constructive criticism. But no one here will volunteer to be a passenger, and the man who owns half the city would rather try to resurrect alchemy as his weapon against the Hurtlers than watch his money disappear into the void.”

“It’s a setback,” Yalda admitted. “But don’t make any decisions right now. Things might look different after a few days.”

Eusebio was unconvinced, but he tried to receive her advice graciously. “Don’t worry,” he said. “I couldn’t throw this all away in an instant if I wanted to. It’s not as if someone’s going to walk up to me tomorrow and offer to buy the mining licenses.”

Yalda woke in the night, unsure for a moment where she was. She raised herself up on her elbows to look around the room. Soft-edged shadows tinged with spectral colors stretched across the floor from beneath the window, framing Eusebio’s sleeping form.

He was beautiful, she realized: tall and strong, perfectly shaped even in slumber. How had she never seen that before?

But it was the thought of him that had woken her. If they brought their bodies together now, she was sure she could extract the promise from him. Her flesh wouldn’t die; she’d let her mind and its anxieties fade away, leaving her children with a devoted protector. He was the closest thing to a co she could hope for, and she did not believe he would refuse her. Not here, alone with her; not if she insisted.

She rose to her feet and stood watching him, imagining his skin pressed against her own, rehearsing the words that would convince him. If Paolo could have six sons, why should Eusebio limit himself to two? She would not say a word against his co; she wasn’t asking him to betray his lifelong partner, only to enlarge his prospective family.

Eusebio opened his eyes. She saw him register her presence, her gaze. She expected to be questioned, but he remained silent, as if everything between them was clear to him already. If she lay beside him now, it would not take much persuasion. They both wanted the comfort of this, and the promise of life for their children.

But as she took a step toward him, Yalda felt a chilling clarity spread across her mind. She wanted comfort—not oblivion. And whatever Eusebio wanted, it was not the encumbrance of her children. Nothing in this beguiling vision had any connection to their real plans, their real needs, their real wishes. The oldest part of her believed it could survive this way—as her mother had survived in her—but even that blind hope was misplaced. Eons of persistence would count for nothing when the sky lit up with orthogonal stars.

She said, “The Hurtlers woke me. I’m sorry I disturbed you.”

Eusebio said, “That’s all right, Yalda. Just try to sleep.” He closed his eyes.

Yalda returned to her bed, but she was still awake at dawn.

After breakfast, Amando came in his truck to take Eusebio to another test launch. Eusebio didn’t demur; the sheer momentum of the project still counted for something. At least until the money ran out.

Nereo walked Yalda to the station. “I’m sorry we didn’t have a chance to talk optics,” he said. “I’ve been tinkering with your light equation recently, trying to find the right way of adding a source.”

“Really?” Yalda was intrigued. The equation she’d come up with five years before described the passage of light through empty space, but said nothing about its creation. “How far did you get?”

“I took some inspiration from gravity,” Nereo said. “Think about the potential energy of a massive body, such as a planet. Outside the body, the potential obeys a three-dimensional equation very similar to the one for light: the sum of the second rates of change along the three directions of space is zero. Inside the body, instead of zero that sum is proportional to the density of matter.”

“So you think I should add a similar term to the light equation, to represent the light source?” Yalda thought about this. “But a light wave involves a vector with four components; the source would have to be the same kind of thing.”

Nereo said, “What about a vector that’s aligned with the history of the light source—pointing into its future—with the length of the vector proportional to the density of the source?”

“That’s the right kind of vector,” Yalda conceded, “but what would this ‘density’ actually be describing?” He didn’t mean mass; this was something else entirely.

“Whatever property matter needs in order to produce light,” Nereo replied. “We don’t have a word for it yet; maybe ‘source strength’? But assuming we can put a number on it, we can talk about how tightly it’s packed: the ‘source density’.”

“Hmm.” Yalda worked through the implications as they entered the station. “So if we’re looking at the simplest case, where everything is motionless, only the time component of the equation would be non-zero, and it would have solutions a bit like gravitational potentials.”

“But not quite the same,” Nereo stressed. “These solutions oscillate as you move across space.”

Yalda’s train was boarding; they didn’t have time to take the discussion further. Nereo said, “I’ll send you a copy of my paper when I’ve written it.”

On the journey back to Zeugma, Yalda managed to find one solution to Nereo’s equation herself: the equivalent of the potential energy around a motionless, point-like mass.

For gravity, it had been known since the work of Vittorio an era and a half ago that the potential was inversely proportional to the distance from the mass. For light, the overall strength of the wave diminished with distance in exactly the same fashion, but it also underwent an oscillation with the smallest possible wavelength—that of a wave traveling at infinite speed. All of this was just an idealization—the need to wrap around the cosmos smoothly would impose additional constraints and complications—but it was a start.

Yalda pondered the curve. Perhaps there was something like this present in everything from sunstone to a flower’s petals. Light at the minimum wavelength would be invisible, so when the source was motionless the petals would be dark. But a system of oscillating sources, suitably arranged, might well be able to twist the original pattern into a set of tilted wavefronts, corresponding to light slow enough to lie in the visible realm.

Exact solutions when the source was in motion wouldn’t be easy to find, but the general idea made sense; to generate a wave that moved energy around, something had to feed in the energy in the first place, whether that meant jiggling the end of a string or vibrating your tympanum in air. That the creation of light would draw true energy out of an oscillating source—increasing its kinetic energy, rather than draining it—was a peculiar twist, but that was rotational physics for you.

There was, Yalda realized, another strange twist, arising from Nereo’s choice of a vector aligned with the particle’s history as the term to add to the equation. If you accelerated a light source long enough to curve its history around a half-circle and send it backward in time… then once it was settled on its new, straight trajectory it would be surrounded by a wave that was the opposite of the original. Compared with its earlier self, the pattern of light the source generated would now appear upside-down.

But how could a featureless speck of matter tell which way it was traveling through time? The arrow of time was meant to come solely from entropy’s rise; a lone particle couldn’t grow disordered. A wave changing sign wasn’t as dramatic as the difference between a stone being smashed and the shards spontaneously reassembling, but it did imply that there might be two distinguishable kinds of source, at least when they weren’t moving too rapidly: one “positive”, one “negative”.

It was evening when the train pulled into Zeugma. Yalda didn’t have the energy to face the four squabbling brats at bedtime, so she wandered around the city center for a while, killing time until she was sure they’d be asleep.

When she finally braved the apartment, she was surprised to find Lidia sitting in the front room, in the dark.

“I thought you’d be at work,” Yalda said. “Did they change your shift—or was there some problem with the helper?” The whole point of asking Eusebio to pay her had been to hire someone to watch the children in her place.

“The helper was fine,” Lidia said, “but we didn’t need her tonight.”

“So you’re working mornings again?”

“No, I’ve lost my job.”

“Oh.” Yalda sat beside her. “What happened?”

“Did I tell you about my new supervisor?”

“The idiot who kept asking you to become his deserted brother’s co-stead?” Yalda didn’t believe the rumor that Lidia had murdered her own co, but there were times when it might have been helpful if more people had taken it seriously.

Lidia said, “Two days ago he came up with a new offer: either I hand the children over to his brother, or he tells the factory owner that I’ve been stealing dye.”

“But you only ever took from the spoiled batches. I thought everyone did that!”

“They do,” Lidia replied. “But he told the owner I was taking good jars as well. He had some kind of paperwork prepared, inventory records that made it look plausible. So the owner believed him.”

“What a piece of shit.” Yalda put an arm across her shoulders. “Don’t worry, you’ll find a better job.”

“I’m just tired,” Lidia said, shivering. “I used to think everything would be different by now—by the time I was this old. But what’s changed? There aren’t even women on the Council.”

“No.”

“Why doesn’t your friend Eusebio do something about that?” Lidia demanded.

“Don’t blame him,” Yalda pleaded. “He’s already fighting the Council on a dozen different fronts.”

Lidia was unimpressed. “The whole point of being a new member of the Council is to fight the old guard and get something useful done. But sharing power never seems to be a priority with anyone.”

“Shocking, isn’t it?”

“Will he have free holin on his rocket?” Lidia wondered. “I might join up for that alone.”

Yalda said, “Of course there’ll be free holin. In fact, it looks as if the entire crew will consist of solos and runaways: one of each, in a rocket the size of this room.”

“That’s beginning to sound less tempting.”

Yalda rose. “I’m sorry about your job. I’ll ask around, see if anyone knows of a position…”

“Yeah, thanks.” Lidia put her head in her arms.

As Yalda crossed the room, a slab of sharp-edged brightness on the floor beside the window caught her eye. The diffuse light from the Hurtlers didn’t look like this; it was as if one of their neighbors had stolen a spotlight from the Variety Hall and mounted it on their balcony.

She walked over to the window and looked out. The neighbors weren’t to blame; the light was coming from high above the adjacent tower. A single bluish point was fixed in the sky, displaying no discernible color trail.

Lidia had noticed the light too; she joined Yalda by the window.

“What is it?”

Yalda suddenly realized that she’d seen the same object high in the east when she’d walked out of the railway station—but it had been a great deal paler then, so she hadn’t given it a second thought. “Gemma,” she said. “Or Gemmo.” The naked eye couldn’t separate them, so there was no point guessing which of the two had suffered the change.

Lidia hummed with exasperation; she was in no mood to be mocked. “I might not be an astronomer,” she said, “but I’m not a fool. I know what the planets look like, and none of them are that bright.”

“This one is, now.” A dark, lifeless world that had once shone by nothing but reflected sunlight was turning into a star before their eyes.

Lidia steadied herself against the window frame; she’d grasped Yalda’s meaning. “A Hurtler struck it? And this is the result?”

“It looks that way.” Yalda was surprised at how calm she felt. Tullia had always believed that a large enough Hurtler could set the world on fire. Dark world, living world, star; they were all made of the same kinds of rock, the distinction was just a matter of luck and history.

Lidia said, “Now tell me the good news.”

Good news? Gemma and Gemmo were far away, and much smaller than the sun, so at least the world wouldn’t suffer intolerable heating from the new star.

In fact, the two planets were so far from the sun that the density of the solar wind in their vicinity was believed to be a tiny fraction of its value around the nearer worlds—and no Hurtlers had ever been seen at such a distance, in accord with the idea that it was friction with that gas that made the pebbles burn up. But the lack of the usual pyrotechnics hadn’t prevented this unheralded impact.

The Hurtlers were everywhere, visible or not—and Ludovico’s absurd explanation for them that blamed the solar wind alone was now completely untenable. Yalda didn’t expect him to recant, but the people who’d voted with him against Eusebio’s offer didn’t have the same degree of pride invested in the matter.

Perhaps the new star was no more exotic than the Hurtlers themselves, but its meaning was far easier to read: the only thing that had spared their own planet so far was luck. Any day, any night, the world could go the same way.

“The good news,” Yalda said, “is that we might just get our flying mountain after all.”

12

“Stay close to me!” Yalda called out to the group as they approached a bend in the tunnel. “Anyone suffering from nausea? Weakness? Dizziness?”

A chorus of weary denials came back at her; they were tired of being asked. She’d been pacing the tour carefully—and the mountain’s interior was maintained at higher pressure than the air outside—but everyone’s metabolism was different, and Yalda had decided that it was better to nag than face a crisis. She certainly didn’t want any of these potential recruits associating the place with sickness.

“All right, we’re now coming to one of the top engine feeds.” For the last few saunters the tunnel had been lit solely by the red moss clinging to its walls, but the illumination from a more variegated garden could already be seen spilling around the bend.

As they took the turn, a vast, vaulted chamber appeared in front of them, a disk almost half a stroll wide and a couple of stretches high. It had been hollowed out of the rock three years before, using jackhammers powered by compressed air; no engines or lamps were employed in the presence of naked sunstone. The usual drab moss and some hardy yellow-blossomed vines covered the arched ceiling, but between the supports the floor was a maze of flower beds luminescing in every hue. Many of the plants were arranged haphazardly, or in small, localized designs, but long strands of cerulean and jade could be seen weaving from garden to garden around the gaping black mouths of the boreholes.

“It wasn’t always so colorful here,” Yalda recalled, “but the construction workers brought in different plants over the years.”

“Will you keep the gardens when the engine’s in use?” Nino asked.

“No—that would interfere with the machinery, and in the long term their roots could even damage the cladding. But these plants won’t be destroyed; they’ll be shifted to the permanent gardens higher up.”

Yalda led her dozen charges to the edge of the nearest borehole and invited them to peer down into the gloom. Far below the chamber, the darkness was relieved by four splotches of green and yellow light; clinging to rope ladders that ran the full height of the shaft, workers wreathed in vines were inspecting the hardstone cladding that lined the surrounding sunstone.

“When the engine is operating,” Yalda explained, “these holes will have been filled-in again, but liberator will be pouring down around the edges. If there are gaps in the cladding, the fuel could start burning in the wrong place.”

“This is the top layer of the rocket, isn’t it?” Doroteo asked.

“Yes.”

“So it won’t be in use for a very long time,” he pointed out.

“That’s true, and I’m sure it will be inspected again before it’s fired,” Yalda said. “But that’s no reason for us to neglect the job now.” Her ideal would have been to prepare every piece of machinery in the Peerless in such a way that the travelers would be able to turn around and come home safely whenever they wished—without requiring any new construction work, let alone any radical innovations. But given the current yield from the sunstone, this top layer of fuel would actually be burned away sometime during the decelerate-and-reverse phase, halfway through the journey. Relying on the status quo would not be an option.

Yalda led the group to a stairwell at the rim of the chamber, and they gazed up into its moss-lit heights. Four taut rope ladders ran down the center—installed early in the construction phase and retained in anticipation of weightlessness—but for now a more convenient mode of ascent involved the helical groove three strides deep that had been carved into the wall, its bottom surface tiered to form a spiral staircase.

“We’ll be climbing up four saunters here,” Yalda warned the group, “so please, take it carefully, and rest whenever you need to.”

Fatima said, “I don’t feel weak, but I’m getting hungry.”

“We’ll have lunch soon,” Yalda promised. Fatima was a solo, barely nine years old; Yalda felt anxious every time she looked at the girl. What kind of father would have let her travel alone across the wilderness, to enlist in a one-way trip into the void? But perhaps she’d lied to him in order to come here; perhaps he thought she was hunting for a co-stead in Zeugma.

The group was evenly split between couples and singles; the singles were all women, except for Nino. Yalda hadn’t interrogated Nino about his background, but she’d formed a hunch that he was that rare and shameful thing, a male runaway.

They began trudging slowly up the stairs; the pitch appeared to have been set to discourage running, should anyone have felt tempted. Their footsteps, and the whispered jokes of Assunta and Assunto up ahead, came back at them in multiple echoes from the underside of the stairs above. Beyond their own presence, Yalda could hear an assortment of odd percussive sounds, creaks and murmurs drifting down from higher levels. The workforce inside the mountain had fallen far below its peak, but it still numbered about a dozen gross, and most of the activity now was in the habitation high above the engines.

“Will the travelers be able to see the stars?” Fatima asked Yalda, trailing her by a couple of steps.

“Of course!” Yalda assured her, trying to dispel any notion that the Peerless would end up feeling like a flying dungeon. “There are observation chambers, with clearstone windows—and it will even be possible to go outside for short periods.”

“To stand in the void?” Fatima sounded skeptical, as if this were as fanciful as walking on the sun.

Yalda said, “I’ve been in a hypobaric chamber, as close to zero pressure as the pumps could produce. It feels a bit… tingly, but it’s not painful, and it’s not harmful if you don’t do it for too long.”

“Hmm.” Fatima was begrudgingly impressed. “And in the sky—will they be our stars, or the other stars?”

“That depends on the stage of the journey. Sometimes both will be visible. But I’ll talk about that with everyone later.” A moss-lit staircase wasn’t the place to start displaying four-space diagrams.

They emerged from the stairwell into a wide horizontal tunnel; this one ran all the way around the mountain, but the nearest junction was just a short walk ahead. Yalda offered no warning as to what lay around the corner; the light gave some clues, but the thing itself always took the uninitiated by surprise.

The chamber was no wider than the one below, but it was six times taller—and the broad stone columns supporting the arched ceiling were all but lost among the trees. High above their heads, but far below the treetops, giant violet flowers draped across a network of vines formed a fragmented canopy that divided the forest vertically. With no sunlight to guide their activity, these flowers had organized themselves into two populations with staggered diurnal rhythms, one group opening while the others were closed. Through the gaps left by the sagging, dormant blossoms, shafts of muted violet reflected back by the stone above revealed swirling dust and swooping insect throngs. Even the air moved differently here, driven by complex temperature gradients arising within the vegetation.

Yalda strode forward through the bushes that had been planted around the chamber’s edge, where the ceiling was too low for trees. “This might look like a strange indulgence,” she admitted. “When we have farms, plantations and medicinal gardens, what need is there for wilderness? But if our survival depends on the handful of plants we’ve learned to harvest routinely, this place still encodes more knowledge about light and chemistry than all the books ever written. Every living organism has solved problems concerning the stability of matter and the manipulation of energy that we’re only just beginning to grasp. So I believe it’s prudent to bring as many different kinds of plant and animal life with us as we can.”

“What kind of animals?” Leonia asked; she didn’t sound too happy about the prospect of sharing the Peerless with a teeming menagerie.

“In here right now, there are insects, lizards, voles and shrews. Soon we’ll be adding a few arborines.” Yalda watched the group’s reaction with her rear gaze; eventually it was Ernesto who said, “Aren’t arborines dangerous?”

“Only when threatened,” Yalda declared confidently. “Most of the stories about them are exaggerated. In any case, they’re our closest cousins; if there are medical treatments we need to test, there’s only so much you can learn from a vole.” It was Daria who’d sold her on most of these assertions—the same Daria who’d made half her wealth from impresarios’ claims about the creature’s ferocity.

Fatima said, “What happens when there’s no gravity? Won’t everything… come loose?”

Yalda squatted down and cleared a small patch of soil, exposing the layer of netting that sat over it. “This is attached to the rock with spurs at regular intervals. The root systems bind the soil together, too—and the soil itself is actually quite sticky. A handful of soil will trickle through your fingers easily enough, but an absence of gravity is not the same as turning everything upside down. What I’m expecting is that the air here and in the farms will grow hazy with dust, but there’ll be an equilibrium where that dust is re-adhering to the bulk of the soil as often as it’s breaking free.”

They took the stairs up to one of the farms, and ate a lunch prepared from the local crops. Wheat adapted well to sunlessness; it grew faster in here than on the farms outside, now that Gemma had all but banished night again. The disruption caused by the second sun varied with the season and the year—and there were periods when it rose and set close to the original, almost restoring normality—but the last Yalda had heard from Lucio was that he and her cousins had given up trying to adjust to the complicated cycle and were simply building canopies over all their fields.

Then it was on to the storerooms, workshops and factories, the school, the meeting hall, the apartments. They ended the day in an observation chamber close to the peak, where they watched the sun setting over the plain below, revealing the mountain’s stark shadow in the rival light from the east.

There was a food hall beside the chamber. Yalda found a free patch of floor among the crowd of construction workers and sat everyone down. Up here they were far enough from the sunstone to use lamps; it might have been any busy establishment in Zeugma or Red Towers.

Yalda dropped her recruiting spiel and let the group eat, with no accompaniment but the sputter of firestone and the chatter of their fellow diners. By now they’d seen not the whole of the Peerless, but at least one example of everything it contained. They’d reached the point of being able to imagine what it would be like to spend their lives inside this mountain.

Leonia, who’d been tense throughout the tour, now appeared almost tranquil; Yalda’s guess was that she’d made up her mind to find an easier way of avoiding her co than fleeing into the void in the company of wild animals. Nino looked haunted, but equally resolved to make the opposite choice. Looking back, Yalda realized that every question he’d asked her had concerned something innocuous or trivial; it was as if he’d wanted to appear engaged as a matter of courtesy, but he’d been so committed to his plan from the start that he’d preferred not to delve into anything that might risk swaying him.

With the others, she was unsure. It was as easy to undersell the problems the travelers would face as to oversell them. Anyone who reached the end of the tour believing that the project was hopelessly ill-conceived would walk away—but equally, anyone who was convinced that the triumphant return of the Peerless was inevitable would have scant motivation to join the crew. Rather than sentencing your descendants to indefinite exile, why not choose the version of events that lasted a mere four years, in which your death far from home was replaced by the imminent arrival of the most powerful allies you could hope for? Of course a Hurtler might incinerate the world before then, but it had been five years since Gemma’s ignition, so it wasn’t hard to imagine the same luck holding out for another five.

In between those two extremes was a sweet spot, where the mission’s potential was beyond doubt but its success remained far from guaranteed—allowing a wavering recruit to imagine their own contribution tipping the balance. Yalda aimed squarely for that result, and she no longer felt guilty or manipulative for doing so. The truth was, though she and Eusebio had filled all the jobs that they knew beyond doubt to be essential, there was nothing gratuitous about raising the numbers still higher—increasing the range of skills, temperaments and backgrounds among the travelers. It was like bringing the forest as well as the farms: the Peerless was sure to find a use for everyone, even if they could not yet say what it would be.

“One came back!” Benedetta shouted ecstatically, running across the sandy ground between the main office and the truck compound. There was a rolled-up sheet of paper in her hand. “Yalda! One came back!”

Yalda gestured to the group to wait for her. She’d been about to take them over to the test site to watch a demonstration launch, but if she understood Benedetta’s cryptic exclamation then this was worth a delay.

Yalda jogged over to meet her. “One of the probes returned?”

“Yes!”

“You’re serious?”

“Of course I’m serious! This is the image it took!”

Benedetta unrolled the crumpled sheet.

Yalda had barely taken in the spatter of black specks when Benedetta turned the paper over to show her the opposite side. It had been marked with three signatures in red dye: Benedetta’s, Amando’s and Yalda’s, along with a serial number, an arrow in one corner to fix its orientation in the imaging device… and instructions to anyone finding it upon its return.

Apart from the image on the sensitized side, Yalda certainly recognized the sheet. It was one of a gross that she’d signed at Benedetta’s request, two and a half years earlier, to guarantee their authenticity.

“Who sent this to you?”

“A man in a little village near Mount Respite,” Benedetta said. “I’ll need your authorization to pay him the reward.”

“Do you know what state the probe itself is in?”

“In his letter he said there wasn’t much left of it apart from a few cogs hanging off the frame, but it was still so heavy that he couldn’t afford to send it to us.”

“Add something to the reward to cover the freight, and get us the whole thing.” Yalda took the sheet from her. “Octofurcate me sideways,” she muttered. “You and Amando really did it.” She looked up. “Have you told him yet?”

“He’s in Zeugma helping Eusebio with something.”

“I never thought this would work,” Yalda admitted.

Benedetta chirped gleefully. “I know! That makes it so much better!”

Yalda was still having trouble believing it. She was holding in her hands a sheet of paper that had left the world behind, crossed the void faster than anything but a Hurtler, turned around and come back… and then traveled here by post from Mount Respite.

“Which stage was it taken in?” she asked.

Benedetta pointed to the serial number.

“Meaning…?” Yalda had forgotten what the numbers signified.

“Odd numbers were for the first stage of the journey, when the probe was traveling away from us.”

“Good,” Yalda managed numbly. She thought for a while. “I think you should come and tell my recruits what you’ve found.”

“Of course.”

Yalda introduced Benedetta to the group, then recounted some of the background to the problem. Years before, she had managed to identify a slight asymmetry in the Hurtlers’ light trails, demonstrating that their histories were not precisely orthogonal to the world’s. This had finally made it possible to say which direction they were coming from; until then, their trails might have marked a burning pebble crossing the sky in either direction. But it had revealed nothing about the Hurtlers’ own arrow of time.

Doroteo was confused. “Why doesn’t their arrow of time just point from their origin to their destination?”

Yalda said, “Suppose you drive toward a railway crossing, and you notice that the track doesn’t make a perfect right angle with the road you’re on; it comes in from the left as you approach the crossing. You might think of the ‘origin’ of the track as being a station that lies behind you, to the left—but assuming that this track is only used in one direction, you still have no reason to believe that the trains will actually be traveling from your left to your right.”

Doroteo grappled with the analogy. “So… we can map the geometry of a Hurtler’s history through four-space as a featureless line, but we can’t put an arrow on it. We can’t assume that the tilt you discovered means the Hurtler’s arrow is pointing slightly toward our future; it might as easily be pointing slightly toward our past.”

“Exactly,” Yalda said. “Or at least, that was how things stood until now.”

Benedetta was shy before the strangers, but with Yalda’s encouragement she took over the story.

The probes had been launched two and a half years earlier: six dozen rockets fuelled by sunstone from the mountain’s excavations, fitted with identical instruments and sent out like a swarm of migrating gnats in the hope that one of them would complete its task and find its way home. Their flight plan had been a less ambitious variation on that of the Peerless, reaching just four-fifths the speed of blue light before decelerating and reversing, with literally just a couple of bells spent in free fall along the way. Compressed air, clockwork and cams controlled the timing of the engines, with opposing pairs of thrusters built into the design to avoid the need to rotate the craft. The aim of the project had been to get an imaging device moving as rapidly as possible, parallel to the Hurtlers’ path, first in one direction and then the opposite.

“This paper was made sensitive to ultraviolet light, about one and a half times as fast as blue light,” Benedetta explained, holding up the travel-worn sheet. “The orthogonal stars all lie in our future, so we can’t expect to see them, or image them under ordinary conditions. But the whole meaning of ‘past’ and ‘future’ depends on your state of motion.”

She sketched the relevant histories on her chest.

“With the probe traveling at four-fifths the speed of blue light, infrared light from the orthogonal stars would have reached it at an angle in four-space corresponding to ultraviolet light from the past.” Benedetta held up the evidence again. “So we’ve managed to record an image of these stars—which to us still lie entirely in the future—by giving the probe a velocity that placed part of their history in its past.”

Fatima said, “How do you know those are images of orthogonal stars, not ordinary ones?”

Benedetta gestured at her chest. “Look at the angle between the light and the histories of the ordinary stars. To them, the light’s traveling backward in time! Only the orthogonal stars could have emitted it.”

Yalda added, “And if the orthogonal stars’ future had pointed the other way, then the probe could only have imaged them once it had reversed and was coming back toward us. So we know the direction of the arrow now—not from the Hurtlers themselves, but from the light of these stars whose origin the Hurtlers share.” This finally put to rest Benedetta’s old fear: that the Peerless might be headed straight toward the orthogonal cluster’s past, requiring the rocket to function while opposing the entropic arrow of its surroundings. Now it was clear that it would not face that challenge until the return leg of the journey.

“And how far away are they?” Fatima asked. “These orthogonal stars?”

Benedetta looked down at the images. “We can’t be sure, because we don’t know how bright they are. But if they’re about as luminous as our own stars, the nearest could be no more than a dozen years away.”

The group absorbed this revelation in silence. Five Hurtlers were spreading lazily across the morning sky, and while Gemma itself was below the horizon, here was a promise of interlopers vastly larger than the baubles that had set that world on fire.

Just when Yalda was beginning to think that the stark new threat might push some of the waverers into making a commitment, Leonia broke the mood. “Six dozen probes went up,” she said, “and this is the only one that’s been recovered? What happened? Did all the others end up as craters in the ground?”

“That’s possible,” Benedetta conceded. “Landings are difficult to automate. But the real problem was returning the probes to this tiny speck of rock from such a distance. The world is a very small target; the tolerances required for attitude and thrust control were close to the limits of what any of us believed was feasible. We were lucky to get even one back.”

“But the Peerless will be traveling much farther,” Serafina noted anxiously.

“With people inside it to navigate,” Yalda replied. “It won’t be down to clockwork to get them home.”

Leonia was unswayed. “Be that as it may, when you rehearsed your great project—on a much smaller scale—you only had one success in six dozen. And you were hoping to impress us by juggling voles!”

The demonstration launch Yalda had arranged would carry six of the animals above the atmosphere, then bring them back down again—hopefully still alive. While clearly no surrogate for the flight of the Peerless, this was not a trivial achievement—and some people did find it reassuring to see that Eusebio’s rockets no longer exploded on launch, or cooked their passengers with the engine’s heat.

“What would persuade you, then?” Yalda demanded irritably. “A full-scale rehearsal, where we send up Mount Magnificent with a crew of arborines?”

Leonia responded to this sarcastically grandiose proposal with a much more modest alternative. “It might mean something if you went up yourself, instead of the voles.”

Before Yalda could reply, Benedetta said, “I’ll do it.”

Fatima emitted an anxious hum. “Are you serious?”

Benedetta turned to her. “Absolutely! Just give me a few days to check the rocket and re-arrange things for the new weight.”

Yalda said, “We need to discuss this—”

“That would be a lot more convincing than voles!” Assunto enthused. His co agreed. “What can an animal the size of my hand tell us about the risks of flight?” she complained. “Our bodies are completely different.”

Yalda looked on helplessly as the group debated Benedetta’s offer; the majority soon reached the view that nothing less would be of interest to them. Only Fatima was reluctant to witness such a risky stunt, while Nino struggled to summon up the appearance of caring one way or the other.

Yalda wasn’t going to argue this out with Benedetta in front of everyone; she sent the recruits off to kill some time at the Basetown markets.

Benedetta was already contrite. “That was poorly judged,” she admitted. “I shouldn’t have sprung it on you out of nowhere.”

Yalda said, “Forget about the timing.” Being made to look foolish in front of the recruits was the least of it. “Why do you think you need to do this at all?”

“We’ve talked about it for years,” Benedetta replied. “You, Eusebio, Amando… everyone agrees it would be a good idea to send someone up—but always later. How long is it until the Peerless is launched now?”

“Less than a year, I hope.”

“And we still haven’t put a single person on a rocket!”

“Flesh is flesh,” Yalda said firmly. “What are voles made of—stone? When it comes to the Peerless, the things we have to worry about will be attitude control and cooling—and we’ve got both of them down to a fine art: in the last four dozen test launches, they’ve worked flawlessly. It’s only the landings that have failed.”

“And only three times,” Benedetta pointed out. “So those aren’t bad odds that I’d be facing.”

Yalda said, “No… but if you did this, what would it actually tell us? Whether you survived or not, how would it make the Peerless safer?”

Benedetta had no ready reply for that. “I can’t point to any one thing,” she said finally. “But it still feels wrong to me to try to launch a whole town’s worth of people into the void, without at least one of us going there first. Even if it’s only a gesture, it’s a gesture that will calm some people’s fears, win us a few more recruits and quieten some of our enemies.”

Yalda searched her face. “Why now, though? You see an image of the future—proof that it’s fixed—and suddenly you’re offering to surrender your life to fate?”

Benedetta buzzed, amused by the implication. She held up the paper from the probe. “If I stare at this long enough, do you think I might spot myself living happily among the orthogonal stars?”

Yalda said, “What if I tell you that I’ve seen the future, and it’s voles all the way?”

Benedetta gestured toward the markets. “Then I can confidently predict that most of those recruits will be gone in a couple of days.”

Silvio stood in the doorway of Yalda’s office. “You need to see this new camp,” he said. “Way out of town.”

She looked down at the calculations Benedetta had submitted on the modified test launch. She’d checked them over and over again, but she still hadn’t made a final decision on whether or not to approve the flight.

“Are you sure there’s a problem?” she asked him. Traders sometimes arrived and set up camp in inconvenient places, but it usually only took them a few days to realize that they were better off in Basetown.

Silvio didn’t reply; he’d given his advice, he wasn’t going to repeat it. It was Eusebio who paid his wages, and if Eusebio put Yalda in charge of the project in his absence then that won her a certain amount of courtesy—but not much.

She said, “All right, I’m coming.”

Silvio drove her a few strolls north along the dirt track that ran from Basetown to one of the disused entrances to the mountain. Yalda didn’t know exactly what he’d been doing there himself; maybe Eusebio had him patrolling the whole area.

There were five trucks at the abandoned construction camp, most of them loaded with soil and farming supplies. A couple of dozen people were visible, digging in the dusty ground. In some respects it wasn’t a bad place to farm, Yalda realized; the shadow of the mountain might well block Gemma’s light enough of the time to allow the crops to retain their usual rhythm, without the need for unwieldy awnings. Having to truck in soil wasn’t promising, but once a crop became established the roots of the plants, and the worms that lived among them, could start breaking down the underlying rock.

Yalda climbed down from the cab and approached the farmers.

“Hello,” she called out cheerfully. “Can anyone spare a lapse or two to talk?”

She caught a few people looking away, embarrassed at the realization that they were being addressed by a solo, but one man put down his shovel and walked over to her.

“I’m Vittorio,” he said. “Welcome.”

“I’m Yalda.” She resisted the urge to make a joke about his famous namesake; either he’d be sick of people doing it, or he’d have no idea what she was talking about. “I work with Eusebio from Zeugma—the man who owns the mines here.” That had become the standard euphemism for the rocket project; everyone knew precisely what was going on inside the mountain, and why, but some people who took a dim view of Eusebio’s whole endeavor were less hostile if they weren’t confronted with explicit reminders of it.

“I don’t believe he owns this land,” Vittorio replied defensively.

“No, he doesn’t.” Yalda tried to keep her tone as friendly as possible. “But if you were hoping to trade with his workers, we have a whole town just south of here where you’d be welcome to set up.” If they signed an agreement with some very reasonable conditions, they could farm just as much land as they were using here, sell their produce in the markets and have access to Basetown’s facilities for no cost at all.

“We chose this location with care,” Vittorio assured her.

“Really? It’s a long way from everything but Basetown, and not as close to there as it could be.”

Vittorio made a gesture of indifference. Other members of his community were watching them discreetly, but Yalda didn’t sense any physical threat, just a mood of resentment at her interference.

“I need to be honest with you,” she said. “In less than a year, this land won’t be suitable for farming anymore.” She was trying to work from the most innocent assumptions she could think of: that the chaos in the sky had driven them off their land in search of some reliable diurnal darkness, and they were unaware of quite how soon it would be before Mount Peerless ceased casting its convenient shadow.

“Are you threatening us?” Vittorio sounded genuinely affronted.

She said, “Not at all, but I think you know what I’m talking about. That you won’t have shade for your crops will be the least of it.”

“Ah, so your master Eusebio will consign us all to flames?” Vittorio made no effort now to hide his contempt. “He’d knowingly slaughter this entire community?”

“Let’s not get melodramatic,” Yalda pleaded. “You’ve barely begun to dig your fields, and now you’ve been informed of the danger so you won’t waste your time putting down roots here. Nobody is going to be consigned to flames.”

“So you pay no heed to the fate of Gemma?”

Yalda was confused. “Gemma is why half the planet has given its blessing to Eusebio’s efforts.”

“Gemma,” Vittorio countered, “taught those of us with eyes that an entire world can be lost to flames. But your master has learned nothing, and in his ignorance he’d blindly set this one alight as well.”

Yalda was growing irritated with the whole “master” thing, but it made a change from being told he was her co-stead. She glanced back toward the truck; Silvio was pretending to be taking a nap.

“You think the rocket would set the world on fire?” If that was his honest belief, Yalda could only admire him for deciding to become a living shield against the threatened conflagration, but he might have dropped by the office and asked a few questions first. “It was a Hurtler that ignited Gemma, and it would take a Hurtler to do the same to us,” she declared.

“A Hurtler, and nothing else?” Vittorio buzzed, amused by her rhetoric. “How can you possibly know that?”

Yalda said, “I don’t know that nothing else could do it—but I know what this rocket will and won’t do. Under the mountain, beneath the sunstone, there’s a seam of calmstone; I’ve been there, I’ve touched it with my own hands. We’ve tested the combination, burning one on top of the other, for far, far longer than they’ll stay together at the launch. The calmstone is ablated by the flame, but there’s no sustained reaction that spreads beyond the site. And before you start protesting that the calmstone is unlikely to be pure, we’ve tested dozens of other rocks as well.”

“And how large was your flame?” Vittorio enquired. “The size of a mountain?”

“No, but that’s not the issue,” Yalda explained. “By holding the flame in place longer in the tests, we can achieve identical conditions in a slab a few strides wide.”

Vittorio simply didn’t accept this. “You’ve played around with some childish fireworks, and you think that proves something. The proof is in the sky.”

“If you’re so impressed by the example of Gemma, how do you propose fending off the Hurtlers that would re-enact the whole thing here?” Yalda demanded. “Thwarting Eusebio won’t spare you from that.”

Vittorio was unfazed. “Do you think there were people on Gemma?”

“No.” This was becoming surreal. “What difference does that make?”

“People can douse small fires,” Vittorio replied. “If one kind of stone is burning, the sand of another kind can be fetched to put it out. If there had been people on Gemma, that’s what they would have done, and that world would not have been lost to the flames.”

Yalda didn’t know how to answer this. To hope that quick thinking and a bucketful of sand could defeat the Hurtlers was absurd… but if you scaled it up to something systematic with teams of rostered observers in every village and whole truckloads of inert minerals at the ready, that might actually contain the effects of a small impact.

“How large is a Hurtler?” Vittorio asked her. He held up two fingers, about a scant apart. “This big? Larger? Smaller?”

“About that size,” Yalda conceded.

“So my choice is between a fire that starts from a pebble, and one that starts from this.” Vittorio turned and gestured at the mountain. “Only a fool would choose the greater risk.”

From the top of the rocket, Yalda could see the wind lifting brown dust from the plain to trace out its eddies and flows. “You can still change your mind,” she said.

“But I’ve already completed the trip,” Benedetta replied placidly. “Time is a circle. It’s happened, it’s over; there’s nothing left to choose.”

Yalda hoped that this fatalist blather was just Benedetta teasing her, but there was no point arguing about it now. The last three of the recruits she’d brought up to ogle the tiny cabin were on the ladder heading back to the ground. Benedetta was strapped onto a bench that had been installed in place of the rack of voles’ cages in the original design; the same cool gases would blow over her body as those that had kept the animals safe from hyperthermia in previous launches. The elaborate clockwork around her that would control the timing of the engines and the parachute’s release had been inspected thrice: by Frido, by Yalda, then finally by Benedetta herself. The voles had only merited two inspections.

“I won’t say good luck then; you won’t need it,” Yalda told her.

“Exactly.”

Yalda couldn’t leave it at that; she squatted down beside the bench. “You know, if you’re made famous by this your co might come looking for you.”

“Whose co?” Benedetta retorted. “Nobody here knows my birth name.”

“No, but how many people as crazy as you could have been born in Jade City?”

Benedetta was amused. “You think I’m from Jade City?”

“Aren’t you?” Yalda had always believed that part of her story. “Your accent sounds authentic.”

“You should hear the other six regions I can do.”

Yalda squeezed her shoulder. “See you soon.” She straightened up then climbed out of the cabin; perched on the ledge above the ladder, she slid the hatch firmly into place. Through the window, she saw Benedetta gesture toward the enabling lever, then make a four-fingered hand: on the fourth chime from the clock beside the bench, she’d launch the rocket. This was the normal protocol, but unlike the voles she’d have to initiate the process herself.

Yalda usually had no trouble with heights, but as she descended the ladder she felt a kind of sympathetic vertigo at the thought of the altitude the cabin would soon reach.

On the ground, she pulled the ladder away and let it fall to one side. The recruits were quiet now; even Leonia was subdued as they started back toward the bunker.

When a gust of wind rose up and sprayed stinging dust into their faces, Fatima said, “Someone should make a truck that runs on compressed air.”

“They should,” Yalda agreed. It had probably been discussed at some point, but then slipped off the agenda; that had happened with a lot of good ideas. Compounding the problem of the project’s sheer complexity, some of Eusebio’s fellow investors had insisted that their funds could only be spent directly on the rocket itself, lest they be viewed as mere secondary players when the descendants of the travelers returned. Yalda found it hilarious that anyone believed that such choices could guarantee them access to the project’s ultimate harvest. If the Peerless really did come back after an age in the void—with the kind of technology that could defeat the Hurtlers and everything that threatened to follow them—they’d trade with whomever they liked, on whatever terms they wished. A certain amount of compassion for their distant cousins was the most she was hoping for; any prospect of scrupulous adherence to contracts signed by their long-dead ancestors was just a fantasy Eusebio had encouraged so the plutocrats could part with vast sums of money without having to confront the horrifying reality that it was actually being spent for the common good.

Frido was waiting by the bunker. “How was she?” he asked anxiously.

“Calm,” Yalda said. “She was joking with me.”

Frido stared back across the plain. Yalda decided that they were the ones who were getting the real taste of cosmic determinism; Benedetta could still decide either to launch the rocket or back out, but nothing her two friends did now could influence her choice.

Everyone clambered down into the bunker. It had been years now since a rocket had exploded at launch, but these precautions weren’t arduous, and though the dust was even thicker down here it was good to get out of the wind.

Yalda lay between Frido and Fatima, watching the mirrored horizon. The rocket was almost lost in the brown haze. She glanced over at the clock; there were three lapses still to go.

Leonia said, “What if she loses her resolve, then regains it? If we come out of the bunker and that thing goes off—”

“That’s not going to happen,” Yalda replied. “She’ll launch at the agreed time, or not at all.”

“What if something jams inside the engine feed?” Ernesta asked. “How can you walk away from that safely, if it might unjam at any time and fire the engines?”

Yalda said, “There’s a backup system to close off the liberator tanks. And if that doesn’t work, Benedetta knows how to take the whole engine feed apart.” Can’t you all be quiet, and just let this happen? She closed her eyes; her head was throbbing.

Time passed in silence. Fatima touched her arm warily. Yalda opened her eyes and looked at the clock. Frido counted softly, “Three. Two. One.”

The radiance of burning sunstone burst through the haze and lit up the plain. Benedetta hadn’t flinched; she hadn’t waited one flicker past the chime. As the rocket rose smoothly into the sky the walls of the bunker shook, but it was no more than a gentle nudge. Yalda felt a rush of empathetic delight. This courageous woman had pushed the lever, and the rocket had done her bidding. Cool breezes would be flowing over her skin, her weight would be no more than half above normal, and with her tympanum held rigid the noise of the engine wouldn’t trouble her too much. Yalda, braced the same way, barely registered the sound of the launch as it reached her.

When the rocket went off the edge of the mirror, Yalda scrambled out of the bunker and stood watching it ascend. Frido followed her, and though she gave no instructions to the recruits everyone soon joined them.

In less than a chime Benedetta would be four slogs above the ground—almost nine times the height of Mount Peerless. From her bench, she would be peering through the window and watching the horizon growing ever wider. Yalda’s skin tingled vicariously at the thought of this foretaste of the greater journey: to ascend and return, without the bitterness of parting from the world forever.

Frido had a theodolite on a tripod set up beside the bunker, but Yalda was content to use her naked eyes, merely checking the time on the clock that sat behind them both. Distance soon dimmed the rocket to a faint white speck, but it was not so pale that there was any ambiguity when the engines shut off and it vanished entirely. Now Benedetta would be weightless, as if she’d stepped into the skin of one of her descendants from the generations who would know nothing else.

The rocket would rise another two slogs before gravity brought it to a halt. As five lapses passed, Yalda pictured it slowing, approaching its peak. Would Benedetta have any way of knowing that she’d reached the midpoint of her journey, apart from the reading on her own clock? How well could you judge your speed, when the landscape that offered the only cues was at such a great remove? Yalda tried to imagine the view from this pinnacle, but the task defeated her. She would have to wait to hear it in the traveler’s own words.

For five more lapses the rocket would fall freely, then the engines would start up again, burning more fiercely than during the ascent, slowing the vehicle sufficiently for the parachute to take over and ease its fall. Yalda kept her rear eyes on the clock and her forward gaze raised to the zenith, trying not to be distracted by the Hurtlers.

Where was the speck of light? She glanced at Frido, but he hadn’t spotted it either. She forced herself to remain calm; the wind was whipping up dust all around them, and it was always easier to track the rockets to burn-out than to catch sight of them as they lit up again.

There! Lower and westwards from where she’d been looking, faint but unmistakable. The cross-winds would have given the rocket an unpredictable horizontal push, keeping it from retracing its trajectory precisely—and Yalda suspected that she’d lost her bearings a little, telling herself that she’d kept her gaze fixed when she’d really been following some slowly drifting streak of color in her peripheral vision.

Frido spoke quietly, his words for her alone. “Something’s wrong,” he said. “It’s coming down too fast.”

Yalda couldn’t agree. He had watched more launches then she had, but he was more anxious too; his perceptions were skewed.

The flame grew closer, its intensity becoming painful; in her mind’s eye Yalda followed it down to a point just a few strolls from the launch site. Benedetta would meet them halfway across the plain, waving and shouting triumphantly.

She waited for the flame to cut out, watching the clock as the moment approached. But when it had passed, the engines were still blazing.

“Something’s wrong,” Frido repeated softly. “The burn must have started late.”

As he spoke, the flame went out. Yalda fixed the clock’s reading in her mind: six pauses after the scheduled time. If the entire burn had been delayed for six pauses, the rocket would have been moving more than ten dozen strides per pause faster than intended when the engines cut out and the parachute was unfurled. Falling faster, from a lower altitude.

“What can you see?” Yalda asked him. The recruits were starting to notice their whispering, but Yalda ignored them and watched Frido searching the sky with the theodolite’s small telescope. The unlit rocket itself would be impossible to make out from this distance, but if the parachute was open the white fabric would catch the sun.

Yalda saw it first—her view was wider, and no telescope was needed. Not a flutter of sunlight on cloth, but the full glare of burning sunstone again. She touched Frido’s shoulder; he looked up and cursed in amazement.

“What’s she doing?” he asked numbly.

“Taking control,” Yalda said. The engines had no provision for manual operation, but Benedetta must have dragged the useless timing mechanism out of the way and re-opened the liberator feed herself.

Fatima approached. “I don’t understand,” she complained.

Yalda addressed the recruits, explaining what she believed was happening. The timer must have jammed for a few pauses while the rocket was in free fall, delaying everything that followed. The parachute must have been torn away when it unfurled at too high a speed. The only way to slow the rocket’s descent now was with the engines. Benedetta would try to execute a series of burns that would bring her to the ground safely.

She said no more; all they could do now was watch and hope. But even with perfect knowledge and perfect control, a powered landing could only be a compromise. You needed to be as low as possible before you finally cut the engines, to spare yourself from the fall—but the lower you descended, the more the ground below you would trap heat from the rocket’s exhaust.

And Benedetta did not have perfect knowledge, just a sense of her own weight to gauge the engine’s thrust and an oblique view of the landscape from which to judge her height and velocity. As Yalda watched, the burn intended to slow the rocket’s fall went on too long; the piercing light hung high above the plain for a moment then rose back into the sky.

The flame went out, leaving the rocket invisible again. Yalda tried to think her way back into the cabin, to regain the sense of empathy she’d felt at the moment of launch. Benedetta had already shown quick thinking and resolve, but what she needed most was information.

The engines burst into life once more, showing the rocket far lower than before. Yalda watched it approaching the horizon, afraid it was not slowing quickly enough, but as it entered the dust haze, sending rippling shafts of light and shade across the plain, her spirits soared. It was easier now to judge its trajectory, and it looked as near to perfect as she could have wished. If Benedetta cut the engines at the lowest point, the fall might be survivable.

The flame dimmed slightly, but it did not go out. Yalda peered into the dust and glare, struggling to discern any sign of motion. Frido reached over and touched her arm; he was looking through the theodolite. “She’s trying to get lower,” he said. “She knows she’s close, but she doesn’t think it’s good enough.”

“Is it good enough?”

Frido said, “I think so.”

Then cut the engines, Yalda begged her. Cut the engines and fall.

The light grew brighter, but it remained in place. Yalda was confused, but then she understood: Benedetta hadn’t increased the thrust, but the rocket was now so low that it was heating the ground below it to the point of incandescence.

Frido let out a hum of dismay. “Go up!” he pleaded. “You’ve lost your chance; give it time to cool.”

The glow flared and diffused. The wind shifted, clearing the haze, and Yalda could see exactly what was happening. The ground was ablaze, while the rocket crept toward it, feeding the flames.

Yalda called out “Down!” and managed to push Fatima toward the bunker before the light became blinding and she stumbled. She lay where she’d fallen, her face in the dirt, covering her rear eyes with one arm.

The ground shuddered, but it was not a big explosion; most of the sunstone and liberator had already been used up. She waited for debris, but whatever there was fell short. When she relaxed her tympanum, all she heard was the wind.

Yalda rose to her feet and looked around. Frido was crouched beside her, his head in his hands. Nino was standing, apparently unharmed; the other recruits were still picking themselves up. Fatima peered out from the bunker, humming softly in distress.

In the distance, a patch of blue-white flame jittered over the ground. Yalda couldn’t tell if it was spilt fuel burning or the dust and rock of the plain itself. She watched in silence until the fire had died away.

“When Benedetta wanted to launch her imaging probes,” Eusebio recalled, “she just wore me down. Six dozen was what she wanted; six dozen was what she got. And if I’d been here for the test flight, it would have been the same. Whatever my misgivings, she would have talked me around them.”

Yalda said, “I wish we’d had a way of contacting her family. Or at least a friend somewhere. There must have been someone she would have wanted to be told.”

Eusebio made a gesture of helplessness. “She was a runaway. Whatever farewells she was able to say would have been said long ago.”

Yalda felt a surge of anger at that, though she wasn’t even sure why. Was he exploiting people, by helping them escape their cos? There was no crime in offering a way out, so long as you were honest about what it entailed.

The hut was lit by a single lamp on the floor. Eusebio looked around the bare room appraisingly but resisted making any comment. Yalda had spent the last ten days here, struggling to find a way to salvage something from Benedetta’s pointless death.

She said, “We need to be more careful with everything we do. We should always be thinking of the worst possibilities.”

Eusebio buzzed curtly. “There are so many of those; can you be more specific?”

“Igniting the planet.”

“Ah, the Gemma syndrome,” he said wearily. “Do you think the farmers rushing to plant crops in the blast zone came up with that themselves? Acilio has people out spreading the idea, and organizing paid relocations.”

“That’s an awful lot of effort just to spite you,” Yalda suggested. “Maybe he honestly believes there’s a risk.”

“A risk compared with what?” Eusebio retorted. “Compared with doing nothing while we wait to slam into a cluster of orthogonal stars? I’ve seen the image from the probe; that’s not a wild guess anymore, it’s a certainty.”

“The worst case,” Yalda persisted, “is that the engines on the Peerless malfunction in such a way that they deliver less thrust than they need to raise the mountain. And they sit there doing it for chime after chime—maybe bell after bell or day after day, if everyone who could shut them down is dead. There must be some point where whatever the Hurtlers did to Gemma would happen here. We’ve done tests to rule that out if all goes well—but we can’t test the most extreme case; there’s no scale model that will tell us what happens when a whole mountain of sunstone sits and burns from below, for days.”

Eusebio rubbed his eyes. “All right, if I grant you all of that… what do you propose?”

“An air gap, all around the mountain.”

“An air gap?”

“A trench,” Yalda explained. “As deep as the lowest engines, and maybe a stroll wide. Then we dig channels under the engines so that all the exhaust gas can escape freely. That would make a big difference to the heat build-up in the rock, if the engines end up running in place.”

“A stroll wide?” Eusebio closed his eyes and swayed backward, fighting not to use indecorous language.

Yalda said, “Look at it this way: a trench that wide would be enough to displace all those irritating farmers—for a reason they can’t really argue against. You could even ask Acilio to help pay for it, seeing as he’s so keen on fire safety.”

Eusebio opened his eyes and regarded her pityingly. “Yes, the need to take a reasonable, consistent position will win him right over.”

“No?”

“Everyone has their own form of vanity,” he said. “You and I enjoy being right: we want to understand how the world itself works, and then humiliate our enemies by proving that their guesses were wrong. Like… you and Ludovico.”

“Hmm.” Ludovico had been dead for a couple of years now, but Yalda couldn’t deny that she’d taken great pleasure in his defeat over the nature of the Hurtlers.

“That’s not Acilio’s nature,” Eusebio continued. “And it’s certainly not how he was raised. In his family’s eyes, the most important event in history was my grandfather cheating them out of a business opportunity that they believed they were entitled to enjoy. And now the family’s honor depends on my humiliation. For that, Acilio doesn’t have to be right about anything; all he has to do is see me fail.”

Yalda was sick of the whole stupid feud, but if Acilio was committed to creating obstacles then they’d just have to find ways around them. She said, “Maybe Paolo will pay for the trench.”

Eusebio stood. “Let me think about it.”

“There’s something more we need to do,” Yalda warned him.

“Of course there is.” He sat again.

She said, “We need a plan, to give people a chance of surviving a Hurtler impact while the Peerless is away. We need lookouts in every village, equipment they can use to try to douse the fire…”

Yalda stopped; Eusebio was shivering. She walked over and squatted beside him, then put an arm across his shoulders.

“What is it?” Not merely the threat of more costs and more work; he had long grown inured to that.

“My co gave birth,” Eusebio said, struggling to get the words out. “That’s why I was in Zeugma; to see the children.”

“She—?”

“Without me,” he said. “Not willingly. If she’d wanted it, we would have done it together. But we waited, and I wasn’t around, so her body just… made its own decision.”

“I’m sorry.” Yalda didn’t know how to console him. She wanted to tell him that she’d been through the same kind of shock herself, but any comparison she made to Tullia would just offend him.

“My father told me it was because I was away so much,” Eusebio said. “If I’d remained close to her, her body would have understood that we were waiting for the right time. But without a co, it gave up hope that the children would ever have a father.”

Yalda wasn’t sure if any of this was real biology, or just a mixture of old folk beliefs and an attempt not to talk about holin. Making the drug available to the crew was one thing, but Eusebio could never admit its use in his own family.

“They do have a father,” she said.

“No, they don’t,” Eusebio replied bluntly. “I still love them, of course, but I’m not promised to them. When I see them, it doesn’t…” He struck his chest with his fist.

Yalda understood. She’d cared for Tullia’s children as well as she could, but for all the genuine moments of joy she’d felt in their presence, she knew it was not the same as the love her father had felt for her.

When Eusebio left, Yalda put out the lamp and sat in the dark. The only certainty lay with the waves that wrapped the cosmos like the wrinkles in her prison sleeve: they would come full circle in agreement with themselves, along with everything they’d built. Nothing else could be relied upon. No one truly controlled their own body; no one ruled over the smallest part of the world.

And yet… it was still in the nature of every person that their will, their actions, and the outcome could be in harmony. That could never be guaranteed, but nor was it so rare that it could be dismissed as a meaningless farce. The will, the body and the world could never be brought into perfect alignment, but knowledge could bind the three strands together more tightly. The right knowledge could have granted Tullia and Eusebia more power over their bodies; the right knowledge could have brought Benedetta safely to the ground.

Yalda was tired of mourning; nothing more could be done for the dead and the divided. The only way to do justice to their memory would be to find the knowledge that would allow the generations that followed them to live without the same risks and fears.

13

Giorgio threw a farewell party for Yalda in his home, a few saunters west of the university. Though she’d been working full-time on the Peerless for six years he had never officially relieved her of her post with the physics department, so it was also a kind of retirement celebration. Zosimo, the only one of her fellow students who had remained in academic life, gave an amusing speech about her early discoveries. “It used to be the case that if you came across someone reading a scientific journal and they kept turning the pages sideways or upside-down, it was a sure sign that they had no idea what they were looking at. Now, thanks to Yalda, it’s proof that you’re in the presence of an expert in rotational physics.”

As Yalda wandered among the guests, she struggled to keep her feelings from turning into grief or self-pity. It might have been better to have vanished without ceremony, but if it was too late for that she could still try to make the break as painless as possible. The day before, she had bid farewell to Lucio, Claudio and Aurelio in a final letter—short and simple, as Lucio had never learned to read as well as his co—but even without this parting note they would not have been expecting to see her again. When Giusto died and she did not visit the family to join them in mourning, they would have understood that she was never coming back. She still wished her brother and her cousins well, but she could not be part of their lives. Now she had to start thinking of her friends in Zeugma the same way.

Daria found her in the courtyard, and instead of offering distracting small talk chose to tackle the subject head-on. “In the old days,” she said, “every dozen generations, families would split up and the travelers would move a whole severance away. With no mechanised transport, that was it: no hope of visits, no hope of returning.”

“Why?” Yalda had heard of the custom, but she’d never understood its purpose.

“They thought it was healthy, to bring new influences to the children.”

“A separation wasn’t enough?” The new farm her father had bought had been that far from the one where she’d grown up.

Daria said, “There was less travel then, less mixing of people for other reasons. This was a way of forcing it.”

Yalda buzzed skeptically. “Was it worth the effort? Were the children any healthier?”

“I don’t know,” Daria admitted. “It’s difficult to study that kind of thing. But every biologist accepts that influences spread from person to person; some make us sick, some make us stronger. I’m glad your travelers will be coming from every city; at least they’ll be starting with a good mixture.”

“So what do we do if the mixture grows stale?” Yalda wondered.

“Learn enough about the things themselves to make new ones of your own,” Daria replied smoothly.

“Ah, as simple as that.” Was an influence a kind of… gas? A kind of dust? How did it leave and enter the body? What exactly did it do when it encountered your flesh? Nobody had the faintest idea.

Daria said, “If the Peerless comes back without that trick, I’ll just have to hang on long enough to work it out for myself.”

“What are you waiting for?” Yalda scolded her. “The Peerless isn’t an excuse for everyone else to take a four-year holiday. You should think of it as a contest; you should be trying to beat the travelers to as many discoveries as possible. We might have the advantage of time, but you’ll always have the advantage in numbers.”

Daria was amused by this idea, but not dismissive. “It would be a matter of some pride,” she conceded, “if we could greet them with at least one triumph of our own.”

Lidia entered the courtyard, accompanied by Valeria and Valerio.

“You missed the speeches,” Daria informed them.

“I’m glad to hear it,” Lidia replied. She embraced Yalda. “Is it true that you’re going to be a Councilor on the flying mountain?”

“Dictator, I think,” Daria corrected her.

Yalda said, “More like a factory supervisor: as far as I’m concerned, my main job will be to ensure that all the machinery is being operated safely. For the first year or two that’s likely to take precedence over everything else, but once the technical issues are under control we’ll have to make arrangements for… ongoing governance.”

“That sounds promising,” Lidia enthused. “In a city of runaways, no one is going to settle for anything less than a fair division of power.”

“Do you want to come and organize that for me?” Yalda pleaded. “Right now, I’m just hoping that any heated disputes can wait until after I’m dead.”

Lidia pretended to be taking the invitation seriously, but it was clear what her answer would be.

The children had been hanging back, waiting for Lidia to finish her greeting. Valerio embraced Yalda awkwardly then went looking for food, but Valeria didn’t flee.

“Are you enjoying your studies?” Yalda asked her.

“I like lens design,” Valeria replied.

“It’s an important subject.” Eusebio had promised to hire Valeria to work on the fire watch project—and cheap, light, wide-field telescopes would be part of the equipment every village would need.

“I brought a gift for you,” Valeria said. She handed Yalda a wooden tube.

“Thank you.” Yalda removed the cap and pulled out a sheet of paper.

“It’s beautiful,” she said, touched and intrigued. “What is it?”

“Do you remember Nereo’s equation?” Valeria asked her.

“Of course.” Yalda had not had the time to do any original work in optics for years—and Nereo himself had died soon after she’d visited him in Red Towers—but she’d been longing to pursue his ideas about the interactions between light and matter.

“You explained it to me,” Valeria said, “three years ago, when I’d just started at the university. And you showed me the solution for a source consisting of a single point—a ‘luxagen’.”

“I remember.” Yalda had been trying to convey to her just how little was still known about the subject, while offering a glimpse of one crack in their ignorance that might yet be widened.

“Not long after that,” Valeria continued, “we were studying gravity. And I learned that the first thing Vittorio did after guessing the potential energy for a mass concentrated in a single point was to calculate what that meant for a mass arranged as a spherical shell.”

“Ah.” Yalda examined the sheet again, overcome with pride and delight. “And this is the equivalent, for the light field?”

“Yes.”

Yalda studied the results. “These sizes you’ve written, they’re the radius of each shell?”

Valeria said, “Yes. Vittorio showed that, outside the shell, the gravitational potential energy was exactly the same as it would have been if all the mass were just concentrated at the center, so I was hoping the light field would follow the same rule. When it didn’t, I thought I’d made a mistake, so I had to wait until I’d learned a different technique that I could use as a cross-check.”

Yalda was still trying to absorb the implications of what she was seeing. “For some sizes of shell… the external field vanishes completely?”

“That’s right,” Valeria confirmed. “That happens whenever the radius is a multiple of half the minimum wavelength. And when it’s an odd number of quarter-wavelengths, the interior field vanishes.”

Yalda would never have guessed that the undulating field from a myriad of point sources could cancel exactly over any extended region—let alone an infinite one, and from such a simple geometry. No wonder Valeria had doubted her first calculations; it was as if someone had claimed that a gross of clanging bells could be rendered inaudible merely by arranging them in a circle of just the right size.

“Have you shown Zosimo and Giorgio?”

Valeria said, “I wanted you to see it first.”

Yalda held the sheet aside and embraced her. “It’s a beautiful gift. Thank you.” Your mother should have been here to see this, she thought, but the words were too strange to speak aloud.

Lidia said, “I don’t want to risk annoying you both… but are these pictures of anything real?”

Yalda started to explain about the light field around the hypothetical particle Nereo had dubbed a luxagen, and how Valeria had added up that field for a multitude of luxagens arranged in a shell, but Lidia hushed her. “I meant something we can all see and touch.”

Yalda thought for a while. What did it mean that luxagens were normally surrounded by furrows in the light field, but in the right configuration the landscape around them could become perfectly flat?

She said, “How about something you can feel, but never see?”

“What, thin air?” Lidia joked.

“Exactly.” Yalda exchanged a glance with Valeria; she looked baffled for a moment, but then she understood.

“Nereo hoped that the light field might account for all the properties of matter,” Yalda explained. “Not just burning fuel and glowing petals, but how a rock holds together instead of crumbling, and how it resists being crushed down to a speck. Why dust is sticky, and fine dust even stickier… but an inert gas like air, which everyone thinks of as the finest dust of all, doesn’t stick to anything, not even itself.”

“And these pictures are the answer?” Lidia was bemused.

“Not to everything,” Yalda said, “but perhaps they’re a clue to the last puzzle. It’s not hard to see how solids could be built from luxagens: the particles would sit in the troughs of each others’ serrated fields, which would hold them a certain distance apart from each other in a kind of array. Two stones you pick up off the ground won’t stick to each other—even if you polish them flat—because with such vast numbers of particles you wouldn’t expect them to form a single, perfect array. But a speck of dust is lighter, and small enough for the internal geometry to be less of a mishmash; there’s more chance for everything to line up and make two specks adhere. So if gases are built from luxagens too—and are so fine as to be invisible—why don’t they stick together even more strongly?”

Lidia still didn’t see it; Yalda looked to Valeria for support.

“Suppose you arrange the luxagens in a spherical shell of just the right size,” Valeria said. “Then the force that makes most regular arrangements of luxagens sticky will vanish outside the shell. A shell like that won’t stick to anything—so maybe that’s what gases are made of.” She hesitated, then turned to Yalda. “I don’t think that quite works, though. If you look at the potential energy curves at the edge of the shells with no external field, they always slope in such a way as to produce an outward force—so wouldn’t that tear the shell itself apart?”

Yalda checked the diagrams. “Ah, you’re right,” she said. “So there must be something subtler going on.”

“See, we don’t have the answers here,” Daria joked. “We need the Peerless to go out and fetch them for us.”

“But this is close,” Yalda insisted. “If it’s not the whole story, it’s still a powerful hint.”

Yalda could have talked optics with Valeria all night, but that would only have made parting more difficult. “Have you seen your brother recently?” she asked.

“Two days ago,” Valeria replied. “I looked after the children while he went to the factory.”

“But you need to study!” Yalda hadn’t meant to blurt out a rebuke, but she couldn’t bear the thought of Valeria jeopardizing her own chances. “You can’t afford to do that all the time,” she added.

“I don’t; Valerio helps too. And Amelio has other friends as well.” Valeria was beginning to look uncomfortable; Yalda let it drop. Lidia and Daria would have helped with the children if Amelio had allowed it, but he was still angry with them for trying to persuade him and Amelia to wait. Yalda would never see Tullia’s grandchildren, but she suspected Amelio would relent in the end and heal the rift with his other honorary Aunts.

Lidia said, “I’m glad I missed the speeches, but I hope I haven’t missed all the food.” Yalda led them indoors, where Giorgio’s children were still running back and forth from the pantry, keeping everyone fed.

Yalda tried to keep the conversation from growing too solemn; she had no intention of making some kind of earnest declaration to each one of her friends, summing up and attempting to put right everything that had passed between them—as if they were business partners settling accounts. She had apologized often enough to Lidia for the unequal share she’d taken in the burden of raising the children, thanked Giorgio and Daria for their help at the times she’d received it, and offered encouragement to Valeria and Valerio whenever it had seemed likely to be well received. There was nothing more she could achieve with a few rushed words, and the last thing she wanted to do was sound like someone making death-bed reparations.

Around midnight, guests began making their excuses. Dozens of people from the university and the Solo Club—acquaintances with whom Yalda had played dice or argued some point of philosophy or physics—bid her good luck with the flight then departed without any fuss.

With the house almost empty, Giorgio approached her.

“Can we see you off at the station?” he asked.

“Of course.”

Yalda had no luggage; everything she owned was in Basetown already, and everything she’d need was in the mountain itself. The six of them walked together down the quiet streets, with Gemma high above them lighting the way.

On the platform, with just a lapse to departure, Valerio started humming and wailing. Yalda was bemused; they hadn’t been close since he was three. She bent down and embraced him, trying to quieten him before anyone else joined in.

“I’m not dying yet!” she joked. “Wait a year and a day, then you can mourn me. But don’t forget that I’ll have had a long life by then.”

Valerio couldn’t really make sense of this, but he recovered his composure. “I’m sorry, Aunty. Good luck with your journey.”

“Look after your brother,” she said. And try not to imitate him.

With her rear gaze, Yalda saw the guard scowling at her; the engine was already running and sparks were rising into the air. She released Valerio, raised a hand to the others, then leaped into an empty carriage as the train began to move.

She sat on the floor, eyes closed, braced against the shock of amputation.

From a distance, Mount Peerless appeared almost unchanged from its pristine state. As the train brought her closer, Yalda struggled to identify anything more than a slight thinning of the vegetation since the first time she’d set eyes on the peak. The mountain roads that had been widened and extended were still invisible from the ground, and even the mounds of excavated rubble from the new trench were lost in the haze.

Basetown was the end of the line. When Yalda walked out of the station the main square was deserted; where the markets had stood just two stints before there was bare, dusty ground. All the construction workers and traders had departed, and though there were probably dozens of Eusebio’s people still around for the final cleanup, on her way to the office she encountered only fellow travelers. As well as inducing an eerie sense that she’d already parted company with the rest of the world, this raised the problem that, out of the six gross or so on the final list of recruits, she’d only managed to memorize a tiny fraction of their names.

“Hello Yalda!” a woman called from across the street.

“Hello!” That she knew the woman’s face only made it more embarrassing.

“Not long now,” the woman said cheerfully.

“No.” Yalda resisted the temptation to take a bet on, “Time to tell your co to buy a telescope!” However good the odds were that this would be apt and welcome, it wasn’t worth the risk of alienating someone who was actually bringing her co along for the ride.

Eusebio was in the office, poring over reports with Amando and Silvio; Yalda didn’t disturb them. Her own desk was almost empty; before she’d left she’d been double-checking calculations for the navigational maneuvers the Peerless would need to perform if it encountered an unexpected obstacle. It looked as if they’d found the perfect route for the voyage—an empty corridor through the void, oriented in the right direction and long enough to take an age to traverse without coming close to a single star—but once they were above the atmosphere it was possible that fresh observations would reveal a hazard that needed to be side-stepped.

She worked through the details one more time. If the obstacle wasn’t too large, they’d be able to swerve around it and still reach infinite velocity—albeit with even less fuel remaining for the rest of the journey than originally planned. There was no way of guaranteeing the Peerless’s triumphant return, but if the travelers failed to attain an orthogonal trajectory—with the Hurtlers tamed and time back home brought to a halt—they would have no advantage left at all.

When his assistants had left, Eusebio approached Yalda. “How did it go with your friends in Zeugma?” he asked.

“It was fine.” Yalda didn’t want him struggling to empathize, telling her that he understood how she must feel. She said, “I think we need name tags.”

“Name tags?”

“For the travelers. Something we can all wear on necklaces, so we know who’s who.”

Eusebio looked harried; Yalda said, “I’ll organize it myself, don’t worry about it.”

“All the workshops are empty,” he said, spreading his arms to take in the whole ghost town. “Not just of people, of tools and materials.”

“Not inside the Peerless, I hope.”

The suggestion appeared to take Eusebio by surprise, but then he found himself with no grounds to object to it. “I suppose that makes sense.” He checked a wall chart. “Workshop seven?”

“Yes.”

Yalda found a spare copy of the recruits list. When she and Eusebio had first set out to sign up volunteers she could never have imagined filling a dozen sheets of paper with their names, but even this final census amounted to less than the population of her home village.

There were still trucks shuttling between Basetown and the Peerless every bell, but they were no longer in high demand; she ended up alone save for a driver she didn’t really know, so she sat in the back by herself and watched the town receding into the haze. She wondered what would happen if she went to Eusebio and said: I’ve changed my mind, I’m staying. There were other people with the skills to take her place in everything she was expected to do; the project would not fall apart on the spot. But she knew she was caught in the trap she’d used herself on so many others: she was vain enough to believe that her presence might make the difference between success and failure. And if the thought of deserting the Peerless to while away four years on the ground waiting for the world’s problems to be solved elsewhere made a thrillingly delinquent fantasy, the one thing she found more terrifying than the prospect of a journey through the void was the possibility of those four years of anticipation ending in silence.

The truck dropped her off at the nearest footbridge. The trench around the mountain was wider than the crevasse that split Zeugma, but this makeshift structure of rope and wood was no Great Bridge. Yalda gripped the hand-rope tightly as she began shuffling over the swaying planks.

The wind from the north was carrying dust from one of the excavation mounds directly toward her, stinging her eyes and skin. Halfway across she stopped, paralyzed. She’d crossed the bridge in stronger winds than this, but recalling those past ordeals didn’t help.

The launch was five days away. It would take her a day to ascend to the workshop, and at least two to make all the tags. By that time, all the travelers would have joined her and the final evacuation of Basetown would have begun. If she entered the mountain now, she would not emerge again.

She hummed softly and tried to picture Tullia beside her, reassuring her. What was she afraid of? Death could claim her anywhere; there was no safe place left in the world. She could keep on dwelling on the dangers of the journey and the bitterness of exile—or she could treat this as a calculated gamble that might lead her to an almost perfect sanctuary: a place where generations could think and study, plan and experiment, test their ideas and refine their methods, for as long as it took to find a way to banish the threat and return home.

If the Peerless had simply been a city in the desert—a city of scholars, a city with free holin, a city with no knife-wielding thugs who could meld her arms together and throw her in a cell—might she not have wandered inside its walls and never come out? Might she not have happily declared: this is the place where I will die?

She steadied herself and walked across the bridge.

The meeting hall had been designed with room for twice the current population of the Peerless, though Yalda wasn’t sure how well the elegantly tiered floor would function later, in the absence of gravity. She stood at the entrance, greeting people as they filed in, handing out name tags from the twelve buckets into which she’d sorted them, along with necklaces from a separate container. The travelers seemed remarkably calm; there was no time to talk with anyone at length, but she’d seen more anxiety on display at some of the recruitment drives in Zeugma.

At the appointed time there were less than two dozen tags unclaimed, and still a chance that some stragglers had merely been delayed. Yalda was astonished; only one volunteer in three dozen had changed their mind and backed out. If she’d been asked a year ago to bet on the chance of her own desertion, she would have put the odds at one in three.

Eusebio was waiting by the stage. He checked the clock and walked over to Yalda.

“Should I start?” he wondered.

“Give it another chime for latecomers,” she suggested. “It’s not as if anyone here will be worrying about baby-sitters charging them overtime.”

Eusebio winced; a man who’d attended one of their free talks in Zeugma had cornered them and demanded payment on precisely those grounds. “Don’t remind me,” he said. “In a couple of stints I’ll be back on the Variety Hall circuit, recruiting for the fire watch.”

“Recruiting?” Yalda was surprised. “Does that have to fall to you? I thought the project had plenty of other backers.”

“There are lots of people spreading the word,” Eusebio agreed, “but we still need to build up support much further, or the whole thing will be too patchy to have any real chance of working.”

Yalda wondered if she should wish him luck with his new endeavor and leave it at that, but then she decided that she had nothing to lose.

“You’re not tempted to join us?” she asked. “No one can see this through to the end, but you could watch over the Peerless for a little longer.”

A flicker of discomfort crossed Eusebio’s face, hardening into defensiveness. “I always made it clear what my role would be. I never promised to do more than build the rocket.”

“I know,” Yalda said mildly.

“I could leave my children if I had to,” he admitted. “It’s my father who’s raising them, more than me. And it’s true that other people would champion the fire watch.” He trailed off.

Yalda fought against an urge to fill the silence, to tell him that she understood his choice and that she had no reason to reproach him for it. She didn’t want to hurt him or embarrass him. But she wanted to hear his whole answer.

“If I joined you,” Eusebio said, “and the Peerless failed… then I doubt that anyone else would have the resolve to try the same thing again. It would still be our only real chance to protect ourselves, but most people would see the whole idea as discredited. That’s why I’m staying. I need to be able to fight for this”—he gestured at the mountain that surrounded them—“all over again, if it comes to that.”

Yalda couldn’t fault his reasoning, but the prospect he was painting chilled her. She should have been happy to imagine a second chance for the people she was leaving behind, but the thought of even the Peerless being dispensable in the end didn’t do much to bolster her justification for her own choice.

She was spared the need to respond; an elderly man was approaching with an apologetic countenance. “I took a wrong turn,” he explained. “This place is a labyrinth.”

“Could you tell me your name, sir?”

“Macario.”

As Yalda fetched Macario’s tag, Eusebio left her and took to the stage. By the time the latecomer had his necklace in place, the hall had fallen silent.

“Welcome back to the Peerless,” Eusebio began. “It’s almost seven years now since I approached my friend and teacher, Yalda, to discuss what could be done about the Hurtlers. At that time, there didn’t seem to be much chance of defending ourselves. We barely understood what we were confronting—and most of what we did know only made us feel more powerless. But now we have the start of an answer. Across the world, the Peerless and its travelers are reason for hope.”

There were lamps throughout the hall, and no lighting technicians here to extinguish them and throw a spotlight on the stage. Yalda watched the audience with her rear gaze as Eusebio thanked them for their courage and commitment. She could see signs of apprehension here and there—bodies hunched anxiously, gazes lowered—but most people appeared steadfast, reconciled to their decision.

“My colleagues and I have worked as hard as we could to ensure that your journey will begin in safety and comfort. But I have never lied to you in the past and I won’t lie to you now: we don’t have the power to promise you anything. In spite of our best efforts, seven people have already died: six construction workers, and a volunteer undertaking a test flight. I can’t guarantee that in two days’ time, this whole mountain won’t be turned into rubble and flames. If anyone in this hall believes that can’t happen, then you should leave and return to your homes, because you are here under false premises.

“My colleagues and I have also tried to anticipate what you and your children will need in order to survive and flourish as the Peerless travels through the void. But nobody has made this journey before. There is no compendium of knowledge on these matters; there are no experts on the territory that lies ahead. If anyone has misunderstood this—if anyone thought that they’d been guaranteed the necessities of life for a dozen generations— then you, as well, should leave and look for those certainties elsewhere, because they are not present on the Peerless.”

Yalda understood Eusebio’s need to speak plainly, but she wondered if he wasn’t going too far. Many people were clearly uncomfortable now, and a few were visibly agitated. It was not that they were learning anything new, but everyone had their own way of dealing with the same difficult truths.

“In two days’ time, if all goes well, you will leave the world behind,” Eusebio continued. “Your fate will be in your hands then, not mine. But the Peerless is a complex machine, and though you have all been trained as thoroughly as possible for your particular duties, only a few of you understand that machine in its entirety. The process of education will continue—and I hope that within a generation or two every adult living in the Peerless will grasp its intricacies more fully than I do myself. For now, though, it is Yalda’s role to determine how best to operate this machine, how to ameliorate any crisis, how to resolve any dispute among you, and how to deal with any other difficulty or controversy that arises. Yalda, her deputy Frido, and whoever else she appoints to assist and advise her, are responsible for keeping you safe, and their decisions must be final. It’s not for me to tell you how the Peerless will rule itself in the eras to come, but as of this moment—and for as long as she sees fit—Yalda must be your sole authority. If you can’t promise her your absolute loyalty and obedience, then leave now, because you are a danger to everyone here.”

Only a few people were discourteous enough to respond to this proclamation by turning to stare appraisingly at Yalda, and she suspected that she was, by far, the traveler least satisfied with these arrangements. But since her omnipotence included the power of delegation, it was probably Frido who should have felt most put upon.

“To those of you I have persuaded to walk away tonight,” Eusebio said, “be assured that you’ve already earned my gratitude and respect, and you will not lose it by reappraising your position. But now I’m done with warnings and discouragement. To all of you who choose to remain—with your eyes open to the dangers and rigors ahead—my message is one of promise. Together, we’ve built this beautiful, intricate seed, and as we prepare to cast it into the void I believe that it has not only the resilience to survive, but also the capacity to grow into an extraordinary new civilization. I am already humbled by your courage and tenacity, but I leave you now with the hope that the achievements of your descendants will be the marvel of all ages. Good luck—and welcome to your home.”

As the audience began cheering, Yalda decided that Eusebio’s judgment had been right after all. If he’d said nothing to remind them of the risks they faced, all his praise would have sounded like empty flattery. Now, even if a handful of people backed out, those remaining could take some strength from the fact that they’d passed one more test of their resolve.

Eusebio called Frido to the stage. “I’m sure that everyone knows their stations for the launch,” Frido said, “but I need to ask you to wait here and confirm them with me, or Rina or Lavinia—they’ll be standing over to my right, shortly. And first of all, anyone leaving us, please come forward and return your name tags.”

A few people began moving tentatively toward the stage. Eusebio spoke briefly with Frido, then embraced him. Frido had told Yalda that it was the sight of his grandchildren that had swayed him into joining her; he’d been paid well enough for his work on the project to ensure that they’d want for nothing, but whatever the prospects for dousing a Hurtler’s fire, only the Peerless offered any hope of dealing with the coming orthogonal stars.

When they parted, Eusebio approached Yalda. “I need to get moving,” he said. “The evacuation’s on a tight schedule. Do you want to walk down with me?”

Yalda’s launch station was three strolls below the hall, almost at ground level. They could spend a day traveling together, reminiscing, exchanging their final thoughts.

“I need to stay here and see how many people we’ve lost,” she said.

“Frido and his staff can reallocate their duties,” Eusebio replied. “You have to trust them to handle things like that.”

“I do trust them,” Yalda said. “But I should be here with them, until everything is sorted out.”

“All right.” Eusebio seemed confused by her decision, but he wasn’t going to argue with her in front of so many onlookers. “Have a safe journey, then,” he said.

“You too.” She buzzed softly. “It’s going to be a long four years for both of us. Just don’t let my descendants find three suns when they get back.”

“I’ll do my best.” Eusebio met her gaze, trying to judge where things stood between them. Yalda let nothing show on her face but simple friendship and a contained sorrow at their parting. There was no untangling the rest of it, no point even acknowledging it now. After a moment, Eusebio stopped searching for anything more.

“Good luck,” he said. He lowered his eyes and walked past her, out of the hall.

Yalda stood watching her new neighbors jostling for access to Frido and his assistants. Out of nowhere, she felt a sudden surge of anger for Daria. With no responsibilities, and so close to retirement, why couldn’t she have come and taught here?

A young solo was standing at the edge of the crowd, one of the recruits who’d witnessed Benedetta’s death. Only two people from that group had chosen to stay with the project.

Yalda walked up to her. “Fatima?”

“Hello,” the girl replied shyly. Though they’d met before, Eusebio’s proclamation of Yalda’s powers had probably rendered her as unapproachable now as the most self-important Councilor.

“What’s your job?” Yalda asked her. “I ought to know, but I’ve forgotten where we assigned you.”

“The medicinal garden. Weeding.” Fatima sounded disappointed, but resigned to her fate.

“But you’ll still have classes. I’ll teach you, if you’re interested.”

“You’ll teach me about light?”

“Yes.”

Fatima hesitated, then added, emboldened, “Everything you know?”

“Of course,” Yalda promised. “How else are you going to end up knowing twice as much as I do? But right now, let’s see if we can find some other people working in the garden with you, then we can all walk down together.”

14

Yalda sat on her bench in the navigators’ post, glancing across the moss-lit room past Frido and Babila to the clock on the wall, waiting for its counterparts to open the feeds and set the depths of the mountain on fire.

The engines that would lift the Peerless off the ground were controlled from three dozen feed chambers that were spread out across the width of the mountain. Within each chamber was a system of clockwork and gyroscopes that regulated the flow of liberator into the sunstone below, taking account of both the overall launch plan and the need to fine-tune the distribution of forces to keep the rocket from tipping or swerving as it ascended. Two machinists watched over each engine feed, ready to perform any simple interventions or repairs, while a network of signaling ropes made it possible to summon assistance from a circle of neighbors, or if necessary from farther afield.

Over the past year, the machinists and the navigators had rehearsed their responses to dozens of possible emergencies. Eusebio and Frido had written the first scripts, and then Yalda and Babila, an engineer from Red Towers, had joined in, until every survivable disaster they could imagine had been prepared for, and the whole team had agreed on the protocols. Well-made clockwork figurines, Yalda had joked, could have done the job in their stead, but then they would have needed a new set of protocols dictating what to do if those figurines jammed.

“Two lapses to ignition,” Frido announced, as if no one else were watching. Basetown would be empty now, and the last train well on its way to Zeugma—though it would not have arrived at its destination before flames began consuming the far end of the track. If someone put their ear to the calmstone rails, they might hear the launch before the vibrations reached them through the looser, heterogeneous rocks below. The Peerless would rise silently above Zeugma’s horizon, bright as Gemma in the eastern sky; the rumble of the ground, the hiss in the air would come later. Standing on the balcony with Lidia and Daria, perhaps Valeria and Valerio would wave to their departing Aunt. Eusebio would still be on the train heading west; Yalda suspected that he would have secured the rear carriage for himself, for the sake of the view.

“One lapse.”

Yalda experienced a sudden, visceral urge to flee—or commit whatever act of violence or supplication it would take to extract herself from danger. But there were no choices now that led back to solid ground, not even for the omnipotent ruler of the Peerless. Frido had let an earlier landmark pass in silence: three lapses before ignition had been the last chance to cancel the launch. Propagating the decree by rope relay all the way to the edge of the mountain might have taken as little as a lapse and a half—if everyone had responded swiftly, without mishap or delay—but in setting the cut-off time they’d erred on the side of safety. For the message to have reached some, but not all, of the feed chambers, leaving the rest to fire on schedule, would have been the worst outcome imaginable.

“Six pauses.”

On this cue Yalda lay back on her bench and strapped herself in place, just as she’d done in the drills. Since Benedetta’s death no one had attempted to reprise and perfect her feat, but two heavily sedated arborines had survived equivalent trips, disgruntled once the drugs wore off but physically intact. Traveling through the void had been shown not to be fatal, in and of itself. And with the riskiest part of the journey—the landing—indefinitely deferred, the odds for the Peerless were not so bad. The only real difference from all the test flights was a matter of scale.

Frido counted, “Three. Two. One.”

Across the mountain, the feeds would be opening now, sending liberator trickling down crevices in the hardstone cladding that protected the fuel. Yalda turned to glance at the clock; only two pauses had passed, and the gray powder had a long way to fall before it reached exposed sunstone. Babila took on the duty of counting the descent: “Five. Six. Seven.”

Yalda braced her tympanum.

“Eight.”

In less than a flicker the wave of compression came hurtling back up through the rock. Through the bench she felt the first insistent tremor from the nearest ignition points, then the pounding of ever more engines reached her until even the most distant were hammering at her body. For one terrified moment she could discern no change in her weight—her skin reported nothing but the bench’s vibrations—then she tried to raise an arm and was rewarded with unambiguous resistance, easily overcome but enough to banish her fears. If the engines had been too weak to lift the mountain, she would not have felt this. No amount of ineffectual flame and fury, no mere buffeting and shaking, could have mimicked the glorious signature of acceleration.

Belatedly, she checked the balance beside her, isolated in a vibration-deadening frame from the jittering floor. The polished hardstone scrood-weight was stretching the spring by close to twice the original amount, putting the thrust within a notch of its intended value. There could be no doubt that the Peerless was rising, climbing ever faster into the sky.

Chilled air flowed through the room; the cooling system was working. Not only had the mountain failed to collapse into smouldering rubble, or squat on the ground building up heat until it set the world on fire, it wasn’t even going to cook its passengers alive.

Yalda’s relief turned to exhilaration. She tried to picture the events below: flame spilling out from the hole the severed mountain had left in the ground, hot gas and burning dust swirling across the plain to engulf the empty buildings of Basetown. If she envied Eusebio anything now, it was the sight of a dazzling white streak of fire splitting the eastern sky, when all she had before her was this trembling red-lit cave. But no matter; she’d write him a note and have it carved in stone to be passed down the ages: You witnessed the launch in all its splendor, but when I looked down on your world it was small as a pebble.

The room shuddered; Yalda was thrown sideways in her restraint, her euphoria banished. She looked to the gyroscopes at the center of the room, struggling to interpret their quivering. She’d sat with Frido and Eusebio, calculating the motion of these devices under all manner of calamities, but now her mind was blank and she couldn’t match what she was seeing to any of those predictions.

Babila caught her eye with a series of symbols on an outstretched palm: One engine failed, but we’ve recovered. That made sense; if the rocket had remained unbalanced and the mountain had started tumbling, the axes of the gyroscopes would have ended up far from their starting markers. The machines feeding the other engines had detected the incipient swerve, and those positioned to compensate were doing so.

One feed had malfunctioned, out of three dozen. That was no worse than the proportion of recruits who’d pulled out. The machinists responsible for it wouldn’t even leave their benches to attempt repairs while the engines were still producing extra thrust, laboring to overcome the world’s gravity. This was failure at a level they’d anticipated, not an emergency. It could wait the six chimes until their weight became normal.

Yalda checked the clock; a single chime had passed. The Peerless would be about a separation above the ground now. She longed for a window—and some magic that would make it worthwhile by granting her a view through the flames—but even the lucky people in the highest observation chambers would only be able to see the distant horizon, gradually shrinking until it was obscured by the glare of the exhaust. By the time their path had curved sufficiently to allow them to look back on their starting point, the world really would appear as small as a pebble.

The room lurched again, a sickening swing abruptly curtailed. Yalda steadied herself and peered anxiously at the gyroscopes; the rocket remained level. Had a second engine cut out, or had the first recovered spontaneously? Even two dead engines didn’t threaten their stability, but ongoing failures at this rate certainly would. Whatever had happened, the machinists on site would leave their benches now, make inspections and report.

Yalda looked across at Frido; he signaled tersely: Patience. Until they had more information there was nothing the navigators could do. The Peerless was still under control, and still ascending at close to the target rate. If that much of their luck continued, in two more chimes they’d reach the point where they could shut down all the engines without fear of plummeting back to the ground. In a wide, slow orbit around the sun, they could assess the situation and make repairs. Dispiriting as such a setback would be, better a delay and some damage to morale than have the Peerless turn into a spiraling firework.

For a third time, the rocket staggered and then caught itself. Yalda felt as if she were back on the footbridge over the trench, paralyzed by the sight of the abyss beneath her—and watching the ropes that supported her snapping one by one. Where were the reports from the machinists? She stared at the bank of paper tape writers connected to the signaling ropes. Though the devices had never been used outside the Peerless, they’d proved invaluable during the construction phase. Only adjacent chambers were connected directly, but messages that needed to go farther could be relayed from chamber to chamber. These particular units had been tested thoroughly—most recently when the machinists had first reached their stations prior to the launch.

Finally, one writer began disgorging a message. Babila could reach it without leaving her bench; she grabbed the end of the strip and peered at it, frowning, before the message was complete. Having the thing print actual symbols would have made it too complicated, so they’d devised and memorized a simple code that could be transmitted by tugging on either of two ropes.

From chamber four, Babila wrote on her palm, stretching her hand to fit more words. Feed stopped. Waiting. Chamber four was out at the rim; the message had reached them via two intermediaries.

That would have been the first failure, with the machinist following the protocol and delaying inspection until the thrust was reduced and movement became easier. But then almost immediately, another message arrived: From chamber three. Feed stopped. Investigating.

Chamber three was also at the rim, right next to chamber four. What source of failure, Yalda wondered, could depend on proximity? Dust from construction rubble—somehow missed in all the inspections—shaken out of its hiding place and rendered airborne by the vibrations?

That made no sense, though. Coarse enough debris might jam the clockwork—delaying the feed’s opening in the first place—but Yalda was sure there was no part of the machinery where grit in the cogs could cause the feed to close once it was already open.

Chamber four, then chamber three… she wasn’t going to wait to learn where the third failure had been. She held up her hand to Babila. Message to chamber two, and all its neighbors: Make a full inspection.

Babila started working the ropes. Frido caught Yalda’s eye.

Sabotage? he asked. His face bore an expression of disbelief. This was not a scenario they’d anticipated.

Just being cautious, she replied. Whatever the cause of the first two failures, it could do no harm to test the assumption that their proximity was more than a coincidence.

Yalda turned to the clock; in a couple of lapses they would reach planetary escape velocity. The protocols dictated that three failures was the limit; one more and she’d have no choice but to shut down all the engines as soon as it was safe and let the Peerless drift around the sun until they’d diagnosed and remedied the problem.

Another of the tape writers started up. This one was out of Babila’s reach; she unstrapped herself and lumbered across the floor, pausing to strengthen her legs with extra flesh from her torso. As she read the message her tympanum twitched, as if she couldn’t stop herself silently cursing. Then she turned away from the machine and wrote across her chest: From chamber two. Intruder sighted. Pursuing.

Yalda and Frido joined her in spreading the news—first to those chambers that were close to number two but where the message would not have been seen already. The rope system was faster than any messenger on foot, but it was beginning to seem hopelessly slow and unwieldy.

When they’d finished Yalda stood beside the tape writers, disoriented and frustrated. An intruder? Accepting the notion was difficult enough, but her role made it even harder to bear. She should have been running through the feed chambers trying to catch the saboteur, not hanging around here playing message clerk.

Six chimes from ignition—precisely on schedule—the other feeds proved that they were operating flawlessly by cutting back the rocket’s thrust from two gravities to one, all the while smoothly maintaining the balancing act compensating for the dead engines. The Peerless was four times as far from the center of the world now than it had been at launch—and moving almost five times faster than it needed to be to continue its ascent indefinitely. To the astronomers tracking their flight from the ground, the journey would appear to be proceeding uneventfully. One more jammed feed, though, and the whole world would have known that they were in trouble.

Yalda tentatively relaxed her tympanum; the hammering of the engines was still unpleasant, but it wasn’t intolerable.

“I think speech is viable again,” she shouted at her companions.

What? Babila wrote on her chest.

Yalda turned to Frido. “So who’s the number one candidate to send in a saboteur?”

Frido’s expression made it clear that he knew who she had in mind, but he still balked at the idea. “Six gross casualties, all innocent people…?”

“If it was Acilio, he wasn’t trying to murder us,” Yalda replied. “If that had been the aim he would have sent someone after the gyroscopes; he could have crashed the Peerless when it was barely off the ground, and made a big display of it for everyone watching from Zeugma.”

“So he wanted us drifting?” Frido suggested. “Demoralised by the engine failures, hanging around in orbit until we’d taken every feed apart and inspected every component a dozen times. Nobody dead, but enough of a setback to humiliate Eusebio.”

“Who’s this Acilio?” Babila asked.

“A Councilor in Zeugma,” Yalda explained wearily. “His grandfather and Eusebio’s grandfather had a business dispute—”

Babila held up a hand to stop her. “I don’t care about anyone’s squabbling ancestors. His name and position should be enough for the people who return to find him and kill him.”

Yalda said, “Yeah, we’re not interested in those barbaric generations-long feuds.”

One of the tape writers sprung to life; Yalda stepped forward and began decoding the message. “From chamber one,” she read. “Intruder captured. Claims he’s alone. Bringing him to you.”

Half a bell later, four machinists entered the navigator’s post. Pia, Delfina and Onesta were walking in single file, carrying their captive on their shoulders; they’d extruded extra arms to hold him in place, but he did not appear to be struggling. The fourth machinist, Severo, was too short to join in the formation, so he walked ahead of the women as a lookout.

The machinists dropped their burden in front of the navigators; the saboteur crouched on the stone, his face turned to the floor. He wasn’t wearing a name tag, but Yalda was almost certain that she recognized him.

“Nino?”

He didn’t reply. She squatted for a better look; it was him. She still remembered handing him his tag before Eusebio’s big speech.

“Why?” she demanded, angry and perplexed. Nino had witnessed Benedetta’s crash, but he had still chosen to stay with them; she’d thought that was a sign of his commitment. “What did Acilio offer you?”

At the mention of the name Nino’s rear eyes flickered toward her, all but confirming her guess. “Is there anyone else here working for him?” she asked.

Nino’s reply was inaudible beneath the noise of the engines. “Speak louder,” Yalda yelled. “Who else did he recruit?”

“I only know about myself,” Nino insisted. “If there are others, I was never told.”

Yalda addressed the machinists. “You did a good job. You should go back to your posts now; I don’t want any feeds left unguarded.”

“Are you sure you can control him?” Delfina asked. “He’s a fast runner. You should fetch some melding resin.”

Melding resin? Yalda said, “We won’t let him out of this room. Please, protect your feeds.”

When they’d gone, Yalda sat on the floor in front of Nino. “Tell me the truth,” she pleaded. “Is there anyone else? If the Peerless ends up damaged, it’s your life too.”

“There are tools in the next chamber,” Babila announced darkly. “Frido could fetch them for us.”

“Tools?”

“Screwdrivers, chisels, awls,” Babila explained.

Yalda said, “Just… let me talk to him.”

She turned back to Nino. “Start at the beginning. If you want us to believe you, you have to tell us everything.”

Nino kept his eyes cast down. “I lied to you,” he admitted. “I have children.”

Yalda recalled him claiming that his co had died when he was young, but she’d never believed that; she’d thought he was fleeing from pressure to raise a family. “So why be apart from them?”

“Gemma destroyed my farm,” he said. “I was already in debt. The Councilor said he’d pay what I owed—and pay my brother enough to look after all the children.”

“In return for what?”

“First, just to join you and… spy for him.” Nino’s voice faltered, though Yalda wasn’t sure if he was ashamed of his actions or merely embarrassed. “I was hoping that might be enough—that I might not have to go into the void myself. But then he gave me instructions for jamming the feeds, and said he’d double the payment to my family if the Peerless went dark within one bell of the launch.”

“How did he know any details about the feeds?” Yalda had forgotten where Nino was meant to be working, but he certainly hadn’t been in training for a machinist’s job.

“I don’t know,” Nino replied. “The Councilor knew more about this rocket than I did. He must have had other spies.”

“Other spies where?” Yalda pressed him. “In the construction crew, or among the travelers?”

“I don’t know,” Nino repeated flatly.

“What did you use to stop the feeds?” she asked.

“These.” He opened two pockets and took out some small rocks. “I jammed them under the emergency shutoff levers for the liberator tanks. I was told to do that for as many feeds as I could, until the machinists got word to shut down all the engines.”

There were several such levers in each feed chamber—some of them far from the machinists’ posts. The chambers were so crowded with equipment that it would have been no great feat to enter and leave them unseen, especially while everyone was confined to their benches.

Yalda took one of the rocks from him. It was a kind of soft powderstone, shedding a fine sand even as she handled it. Jammed under a lever, before long it would have simply crumbled and fallen away. If Nino hadn’t been caught in the act they might never have known what had really happened, and ended up convinced that the feeds themselves were at fault.

“And then what?” she asked.

“Nothing else,” Nino said. “If I didn’t get caught, I was meant to blend in again: just go back to my station and do my job.”

“So after the sabotage was over, you’d be ready to pull your weight?” Yalda asked sarcastically. “Ready to be part of the team again?”

“I never wanted to harm anyone!” Nino protested vehemently. “The Peerless was meant to drift in the void for a while—that’s all. Once the Councilor got what he wanted, why would I bear any ill will toward you?”

“Whatever your background really is,” Yalda replied, “you’ve seen more than enough since we recruited you to know how dangerous this was. Don’t pretend that it never crossed your mind that you could have killed us all.”

Nino tensed angrily at the accusation, but his silence stretched on too long to end in an indignant denial. “I asked the Councilor about that,” he admitted finally. “He said if the mountain crashed into the ground, it would be a mercy.”

“A mercy?”

Nino looked up and met Yalda’s gaze. “He said the whole idea of a city in the void was insane. One by one, things would go wrong—things that couldn’t be fixed without help from outside. Within a generation you’d all be starving. Eating the soil. Begging for death.”

Yalda sent a message up to the nearest construction workshop, summoning people with the skills to create a secure prison cell, but she expected it would take a couple of days for them to arrive, lugging supplies. As a stopgap she shifted the food out of the pantry that served the navigators’ post and improvised a latch for the door, using tools and spare parts from the adjacent feed chamber. The navigators would be sleeping in shifts, so there would always be at least two of them awake—and by moving the bed right next to the pantry door, it provided a barricade and allowed even the sleeper to act as a third guard.

Babila had offered to escort Nino up through the mountain and organize his incarceration in a distant storeroom—for the sake of getting him as far away as possible from anything vulnerable to further sabotage—but Yalda preferred to have him nearby, in case she thought of something important that she’d failed to ask him about Acilio’s scheme. According to the recruitment records Nino was unschooled, but as an experienced farmer he’d been destined for the same job on the Peerless. Yalda had no reason to trust him to tell the truth about anything, but his account of his own actions struck her as plausible, even if he was probably embellishing the story or omitting details in order to portray himself in the best possible light.

As her sense of shock and anger faded, Yalda found herself feeling a kind of battered exhilaration at the way things had actually unfolded. The Peerless had been tripped, three times, but it had kept its balance—and if the test had been unwelcome, the outcome was still worth celebrating. They had proved that the machinery on which their lives depended was every bit as resilient as they’d hoped—and they had humiliated an enemy in the bargain.

Perhaps she and Eusebio had been foolish not to anticipate how far Acilio would go. But what more could they have done to protect themselves? Hired people to travel the world and check every crew member’s story? That would have done wonders for the recruitment rate—and told them nothing of value, since every runaway lied, with good reason.

If Nino’s actions really were the end of it—the old world’s last feeble swat at the new—that was cause for celebration, too. As Daria had said, separation was painful, but it was time to break away from the old influences.

We can’t spare his life, Frido told Yalda, raising the words across his chest. Perhaps his silence was out of concern for the prisoner’s feelings—but then, Babila was sleeping, and they all grew tired at times of shouting over the sound of the engines.

Why not? Yalda wasn’t surprised by his advice, but she’d been dreading its eventual arrival from some quarter or another.

Once we have all the information we can get from him, Frido replied, the most important thing is deterring anyone else in Acilio’s pay. If we can’t find the other agents, the next best thing is to make them too afraid to act.

Yalda did not find this persuasive. Once we’re no longer visible from the ground, Acilio has no stake in doing anything more to us. Whatever setbacks we suffer, they can’t embarrass Eusebio if they go unseen. And even if Acilio did want to harass us further, how could any agent be rewarded for carrying out his wishes when the payoff couldn’t possibly depend on it? She could understand Acilio’s deal with Nino: even if Nino had no way of seeing it honored, his brother could have gone to Acilio and said “Everyone knows the rocket went dark, so where’s the money you promised us?” But given that Acilio had made no effort to annihilate the Peerless at launch, she couldn’t see him offering a second saboteur money for his family conditional on the Peerless failing to return at all.

You may be right about that, Frido conceded, but even if Nino wasn’t trying to kill us, he certainly betrayed us. He has no place among us anymore. People won’t accept anything less than his death.

“So are you planning on staging an uprising if I don’t agree?” Yalda hadn’t trusted her intended sarcasm to come across in symbols alone, but after shouting the words over the engine noise she wasn’t sure that the shift in modes had been particularly helpful.

“All I’m saying is that it will weaken your authority,” Frido shouted back.

So I should kill a man for the sake of my authority?

Frido considered the question seriously. I suppose that depends on how many people you think will die, if you lose control here.

Yalda said, “I don’t flatter myself that I’m the one pillar of sanity that can keep the Peerless on course.”

“I’m not suggesting that either,” Frido assured her. But whenever power changes hands, there’s a risk of violence—unless you just resign at the first hint of dissatisfaction.

Yalda didn’t know how to reply to that. Did Frido covet her position? It had been less than two days since the launch, less than four since Eusebio had given her this role. She found the burden so unwelcome that the thought of anyone aspiring to take it from her had never crossed her mind before. But if it was so unwelcome, perhaps she should relinquish it? If Eusebio had appointed Frido ruler of the Peerless she would never have objected; why not correct his decision before anyone grew too attached to the status quo?

And then instead of Nino dying to keep her in power, he could die to give her an easy life.

The observation chamber was a shallow cave cut into the side of the mountain, sealed against the void by a tilted dome of clearstone panes. Standing at the edge of the cave, Yalda gazed down the slope and confirmed that the plains from which the mountain had once risen truly were gone. A haze of scattered light from the engines spilt past the rim of the mountain’s base, like the harbinger of some spectacular dawn, yet it was above that glow—though still unprecedentedly downhill—that the blazing sun was now fixed. Yalda stretched out her arm, and with her rear eyes saw the shadow it cast on the roof of the cave.

The polygons of clearstone around her had become pitted by debris during the launch; the flaws caught the sunlight, creating distracting specks of brightness that competed for her gaze with the true sky beyond. She would have struggled to locate her target, had she not known in advance where to search for it: about halfway between the sun and the “horizon” implicitly defined by the chamber’s floor.

To her naked eye the slender crescent cradled a disk of featureless gray, but through the theodolite’s small telescope the planet’s night side was revealed as an elaborate patchwork of hues. She recognized a few tiny splotches of pure wheatlight, but mostly the colors of the forests and fields were woven together too tightly to separate. She thought of Tullia—on the peak of this very mountain, not so long ago—hunting for the spectral signature of plant life on other worlds.

No cities were visible at this remove. No wildfires, either; even if the crater the Peerless had left behind was still smouldering, here was proof that the launch had not created another Gemma. Yalda shuddered, imagining for a moment how it would have felt to look back and discover that everything they’d been fighting to protect had been consigned to flames.

She recorded the bearing from the theodolite’s dials, then took sightings of Gemma, the inner planet Pio, and a dozen bright stars. Four Hurtlers were visible, long gleaming barbs skewering the scene like the tools of a blind but indefatigable assassin. Clockwork and gyroscopes wouldn’t be enough to guide the Peerless safely to its destination, the empty corridor where it could drift for an age without fear of being stabbed from any angle. Only a routine of meticulous observations, calculations and adjustments could lift the odds of a successful journey above those of Benedetta’s automated probes.

The calculations took more than a bell, but the results were encouraging: the Peerless’s position and orientation were very close to the values specified in the flight plan, and the small adjustments she’d pass on to the feed chambers would easily nudge the vehicle back toward that ideal path.

Yalda was reluctant to leave. She aimed the telescope at her old home again, trying to commit its unfamiliar face to memory. On the ground, there’d been farewell after farewell, but this was the final parting.

As a pang of loneliness grew in her, she tried to assuage it by confronting the subject directly. If she’d had the chance to bring anyone she wished along with her, who would she have chosen? Eusebio and Daria would have been enough to keep her company, she decided; better that Lidia and the children, Giorgio and his family, Lucio and the others all stayed put. If everyone she cared about had come along for the ride, she might have felt tempted to abandon the idea of the Peerless ever returning, content to imagine this fortunate few, safe and self-sufficient, drifting on through the void with their rear eyes firmly shut.

Satisfied that the emergency had passed and no more saboteurs were likely to emerge in her absence, Yalda decided to take a short trip up through the mountain. She’d received news of some minor damage via the rope network, and though the repairs were reportedly proceeding smoothly she wanted to see how things stood for herself.

One of the feed chambers for the second tier of engines had suffered a partial ceiling collapse during the launch; it had been empty at the time, so no one had been harmed. When Yalda arrived a work team was still shifting rubble, and Palladia, a former mining engineer who’d been involved in the construction phase, was on site assessing the damage and making plans to insert a new supporting column.

“Can you fix this in five stints?” Yalda asked her. The second tier wouldn’t be firing quite that soon, but as well as having its damaged parts replaced the feed mechanism would need to be cleaned, inspected and tested—none of which would be possible while there was building work going on.

“Three stints,” Palladia promised her. Yalda looked around the chamber at the women and men with wheelbarrows, shovels and brooms, collecting up everything from fist-sized chunks of hardstone cladding to innocuous-looking streaks of powdered sunstone that had fallen through the broken ceiling from the surrounding lode. If the liberator tanks had ruptured, innocuous would not have been the word for it.

“I think it’s good for morale that there’s something to be fixed,” Palladia mused. “Once you’ve repaired a building with your own hands, you really have a stake in it.”

“You could be right,” Yalda said. Nobody wanted to feel like a caged vole that Eusebio had tossed into the void, a breeding animal who was only here for the sake of their remote descendants’ accomplishments. “Still, I wouldn’t hope for too much more of the same.”

“The kind of compressive forces that the launch produced here won’t ever be repeated,” Palladia replied, “but when the weight of the mountain vanishes entirely, that will be an experiment we’ve never really carried out before.”

When the workers took a meal break, Yalda sat and ate with them, joining one group in a quick game of six-dice. The pantries on every level had been stocked with loaves—and holin, which the women passed around unselfconsciously, as if it were some kind of condiment. The few men in the team, most of them accompanied by their cos, appeared comfortable enough in this strange new milieu, and if anyone was suffering regrets over the ties they’d severed, the camaraderie here surely dulled the pain.

After the meal the cleanup resumed, but Yalda was out of synch with her hosts and in desperate need of sleep. When she woke she bid Palladia and the crew farewell, and continued her long trudge upward.

The moss-lit staircase stretched above her interminably, the view barely changing as she ascended. The higher engine tiers were undamaged—or at least, they’d passed a superficial inspection, and any further attention could wait until the second tier was in perfect shape—so she’d have no cause to linger in those deserted chambers. She could still hear the sound of the engines below, but distance took the annoying edge off it, leaving an almost reassuring buzz.

With no company, she passed the time sorting through a long list of anxieties. Would these runaways do a better job of raising their friends’ children than she’d done with Tullia’s? At least the fatherless wouldn’t be a derided minority here—but if that were the deciding factor, what would be the fate of the fathered few? Then there was the transition that would inevitably follow: the rebalancing of the sexes in the next generation, bringing problems of its own. The Peerless had been a gift to runaways, but from here there was nowhere to flee. The only hope for their children would come from instilling the principle of autonomy so deeply that no one had reason to fear their own co.

When she reached the first level above the highest engines, Yalda unbarred the safety doors and stepped out of the stairwell; a short tunnel with three more sets of doors took her to the edge of the cavern. The arborines would have no reason to leave the most comfortable place in the Peerless for them, but she wouldn’t have wanted a confused animal rampaging through the feed chambers below.

She stood among the bushes watching a nearby tree, one branch trembling as two lizards ran along it chasing mites. It had taken so much work to construct this buried forest that when it had first shown signs of flourishing—long before the launch—she’d felt as if they’d already succeeded in bringing the whole world with them into the void. But if that sentiment had been premature, at least the launch appeared to have done no harm here; the trees had proved resilient enough, and the lizards looked as vigorous as ever. She wouldn’t seek out the arborines to inquire about their health, having seen the kind of mood they were in after the test flights—but those flights had included greater accelerations than the Peerless had experienced, and still caused the creatures no injuries.

The faintly rotting smell of the place was not quite the same as any odor Yalda recalled from childhood, and the violet light reflecting back from the ceiling was more eerie than nostalgic. Still, it might be good for people to come here now and then to remember—or in later generations, to imagine—the world from which this small, imperfect sample of life’s richness had been plucked.

Yalda had received no reports of damage to the farms, but she stopped at one of the caverns of wheat to inspect the crop with her own eyes. Like the forest below, this field had been established for years, so if it had survived the briefly elevated gravity there was no reason to think it couldn’t go on thriving. Half the red flowers were open and shining healthily, while the other half slept. As she walked between the rows, alone, she noticed an occasional broken stalk or disheveled flower, but none of the plants had been uprooted. She’d seen worse than this back home after a few stiff gusts of wind.

There’d been a ceiling collapse in one of the medicinal gardens, so Yalda made that her next stop. As she walked down the tunnel from the stairwell, the drab glow of the moss gave way to a richer light than even the forest had offered, and her first glimpse revealed a lush, vibrantly colored mosaic of plants spread out across the cavern. It was only when she reached the entrance that she saw the pile of rubble to her left, and the dozen or so people trying to clear it without trampling any of the precious shrubs.

Yalda approached the group, calling out a greeting. Everyone acknowledged her politely, but only one of the workers offered more than a deferential nod.

“Yalda! Hello!”

“Fatima?”

Fatima walked over to her, picking her way carefully through the debris and crushed plants.

“Was anyone hurt?” Yalda asked.

“No, we were all in the dormitory when it happened.”

“That’s something.” Yalda looked up at the ceiling, which had lost a chunk the size of a small house; they were above the sunstone lode here, so the walls had no need for protective cladding, but the natural mineral formation exposed by the original excavation must have been less stable than the engineers had thought. “What about the plants?”

Fatima gestured at the rubble. “All of that used to be soldier’s ease.” Yalda knew the blue-flowered shrub, which had grown wild near the farm; its resin helped with wound-healing, though some less-than-helpful chemist had found a way to modify it to produce the melding formulation so beloved of the police.

“Don’t take it too badly,” Yalda said. “There’s plenty more in the other gardens, and you’ll get it started here again in a stint or two.”

Fatima didn’t actually appear grief-stricken by the loss. “We’ve really left the world behind?” she asked.

“Absolutely,” Yalda assured her.

“You’ve looked back and seen it?”

“Yes.” Yalda was sure that Fatima understood perfectly that if they had not reached the void they’d simply be dead—but with the weight of everything restored to normal, nothing in this cave conveyed the truth to her senses. “You should see it for yourself. All of you. Who’s the supervisor here?”

“Gioconda.” Fatima pointed her out.

Yalda approached the woman and asked her how the work was proceeding, then negotiated a break in a bell’s time when anyone who wished could come with her to the nearest observation chamber.

“I’d like to see the world, myself,” Gioconda said. “Before it’s too faint.”

While they waited, Yalda helped shift the rubble. Gioconda was planning to use it to build a series of paths through the garden—covering the bare soil between the plots that currently provided a sanctuary for weeds—but the larger pieces of stone would need to be broken up, and all of the paving would need to be bound to the netting so it would remain in place when the Peerless ceased accelerating.

The work was relaxing, and the team seemed to be in good spirits. Once the schools started up, Yalda decided, it would not take much more to make this flying mountain as good a place to live as any small town. It would never match Zeugma’s range of cuisines—or be visited by touring entertainers—but there was nothing to stop people inventing their own new dishes, or devising their own variety shows.

The observation chamber wasn’t far; the edge of the mountain was less than a stroll away, and then a short descent took them to a clear-domed cave much like the one on the navigators’ level. Yalda hadn’t come prepared with coordinates, but she managed to locate the world’s tiny crescent without too embarrassing a delay.

The gardeners lined up to take turns looking through the theodolite, and Yalda watched their faces as they stepped away, silent and reflective. The ultimate purpose of the Peerless was more remote than ever now, with the site of its hoped-for return promising only to fade and vanish, never to be seen again in their lifetimes. But Yalda detected no signs of despair. They were not of the world anymore, but they had their own home to advance and protect. Best of all, even in parting they had not become rivals or deserters: if the Peerless flourished, the old world would share the rewards.

When everyone had seen what they’d come here to see, Yalda showed them Pio’s stark terrain, then Sitha’s glorious color trail.

“When will we be able to see the orthogonal stars?” Fatima asked impatiently.

“Not for a while yet,” Yalda replied. “So far we’ve barely changed the angle we make with starlight.” She looked around the chamber at the others. “Is there anything else someone would like to see?”

One of the gardeners, Calogera, gestured toward the barren slope beyond the dome. “I’d like to see the traitor Nino falling past: thrown off the peak of the mountain, on his way down into the engine’s flames.”

Yalda didn’t speak until the cheering stopped, which gave her time to decide that it would be best not to respond at all. “I’ll need to get moving now,” she said. “I have more inspections to perform. I wish you well with your repairs.”

Yalda returned to the navigators’ post. A cell had been constructed in a corner of the room, but the builders had rendered it inconspicuous, the wall blending seamlessly with the original, the triple-bolted door almost invisible. Frido and Babila had been opening the small hatch and tossing in loaves without exchanging a word with the occupant, and with a floor of soil packed with worms to eat the prisoner’s faeces, there really was no reason the door would ever need to be opened.

It took Yalda two days to work up the courage to pull the bolts and step into the cell. They weren’t torturing their prisoner with darkness; the walls here emitted the same mossy red glow as they did outside. Nino sat, unrestrained, in a corner; he did not look up as she closed the door behind her and approached.

Yalda sat on the floor in front of him. “Is there anything you want to say to me?” she asked.

“I’ve told you everything,” Nino replied dully. “If there are other saboteurs, the Councilor never mentioned them to me.”

“All right. I believe you.” Why would Acilio have told this man anything, beyond the instructions he needed to complete his own task? “Your confession is complete. So what now?”

Nino kept his eyes on the floor. “I’m at your mercy.”

“Maybe,” Yalda said. “But you must have your own wishes.”

“Wishes?” Nino made it sound like an infant’s nonsense-word.

“If you had a choice,” Yalda persisted, “what would your fate be?”

Nino took a while to respond. “Never to have listened to the Councilor. Never to have got into debt. Never to have seen a second sun in the sky.”

“That’s not what I meant.” Yalda had imagined the conversation proceeding very differently. “You’re here, you’ve done what you’ve done, we can’t change that. So what now? Do you want an end to it?”

Nino looked up at her, shocked. “Nobody wants to die,” he said. “It’s what I expect, but I’m not going to beg you for it. I’m ashamed of what I did, but I haven’t lost all dignity.”

“No?” Yalda spread her arms to take in the cell. “What dignity remains for you here?”

Nino glared at her, then touched his forehead. “I still have my mind! I still have my children!”

“You mean, you have your memories?”

“I have my past,” Nino said, “and their future. My brother will struggle without the Councilor’s second payment, but I know he’ll do his best.”

“So… you’ll just sit here and imagine their lives?”

“With pleasure, for as long as I’m able,” Nino replied defiantly.

Yalda was ashamed. She had tried to convince herself that she’d be offering him mercy, but in truth that logic was as odious as Acilio’s. She had once believed that she faced a lifetime in chains herself, convinced that no one with the power to help her would ever give a thought to her plight. In the darkness of her cell, with Tullia’s encouragement still fresh in her mind, she’d guessed the shape of the cosmos, no less—but robbed of any further companionship she doubted that her mental discipline would have persisted for long. Nino, too, had the life of the mind to sustain him for now, but it wouldn’t last forever.

Yalda left him. She stood at her desk, pretending to pore over a star chart, ignoring Frido’s enquiring glances.

What did she owe the crew of the Peerless? Safety, above all else, but Nino’s death wasn’t necessary for that. The satisfaction of revenge? It would please most of them to see him die, but did she owe them that pleasure?

And what did she owe Nino? He had been weak and foolish, but had he forfeited his right to live? When Acilio had dragged her into his stupid feud, her own pride had lost Antonia her freedom. Who was she to declare that Nino’s crime was so great that he deserved no mercy whatsoever?

But if she did spare his life, that would not be the end of it. If she kept him locked up, she couldn’t banish him from her thoughts and pretend that his welfare and sanity were not her responsibility.

She stared down at the chart, at the few crosses marked near the beginning of a course that stretched past the edge of the map. What did she owe the generations to come, who’d follow the path set by her bearings? The hope of a notion of justice less crude than their ancestors’, where a few well-placed bribes and a sergeant’s whims could bury anyone in a dungeon for life. She owed it to them to set her sights higher.

Yalda looked over at Frido. “There isn’t going to be an execution,” she said.

Frido wasn’t happy, but he understood from her demeanor that there was no point arguing. “It’s your decision to make,” he replied. “Do you want him sent up the mountain?”

Yalda said, “Not while I’m down here.”

“You still need to question him?”

“No. He has nothing left to tell us about Acilio.”

Frido was confused. “So why keep him here?”

Yalda noticed that they’d woken Babila with their shouting, but she needed to hear this too.

“If I’m going to take his freedom away,” she said, “then it’s up to me to deal with the consequences. I’m going to need to find a way to keep him busy.”

“Busy how?” Frido protested. “He’s a farmer, not an artisan; you can’t turn his cell into a workshop.”

Yalda said, “I wasn’t thinking of anything so ambitious.”

Babila rose from her bed. “Then what?”

Yalda said, “Where do we start with anyone? If our records are correct, he’s never been to school. So the first thing is to teach him how to read and write.”

15

When the world disappeared into the glare of the sun, Yalda was relieved; the long farewell was finally over. A stint later, when she returned to the observation chamber, even Gemma had vanished to the naked eye. Through the theodolite’s telescope, sun and erstwhile planet were just another double star, a bright primary and its fainter companion, with fringes of violet and red destined to spread into a full-blown color trail. If any Hurtlers were lighting up the skies of her old home, sheer distance had rendered those threads of color too faint to discern at all.

Yalda made her measurements and calculated the adjustments needed to keep the Peerless on course. As far as she could see they were heading for a region of unblemished darkness, but that was not a judgment to be made from her vantage, handy for directing the feed chambers but compromised by the haze that spread up from the engines’ exhaust. Near the top of the mountain, in the pristine void, a team of astronomers were using the original telescope that Eusebio had bought from the university to scrutinize the corridor as they approached it. Whatever improvements in optics the future might bring, now was the time to confirm that the path they’d chosen for their long, straight run would be empty of ordinary gas and dust; once they were traveling at full speed any such obstacles would be like Hurtlers, with histories—by the travelers’ reckoning—stretched momentarily across an expanse of space, impossible to detect in advance.

To Yalda, this encroaching blindness was both perfectly explicable and utterly strange. The line of sight between the Peerless and the region they planned to traverse would remain unobstructed—but as their history curved toward the corridor, their gaze would be forced away from it. Nature had granted everyone both front eyes and rear, but that symmetry only held in three dimensions; in four-space, you could only look back. Right now, light scattered long enough ago from any dust that lay ahead could reach them at an angle in four-space that made it, on their terms, light from the past. But all too soon, light from such a source would be arriving from their future—so if it did fall upon their eyes, rather than absorbing it they would be emitting it.

There was no fundamental reason Yalda could see why a living creature could not have possessed the ability to perceive the emission of light from its body—but the ordinary conditions of motion and entropy under which life had arisen would have rendered such a talent useless. The kind of sense organs that might have granted her arborine ancestors a view of the orthogonal stars eons in advance would not have helped them see which way a lizard was going to jump five flickers into the future.

The things worth knowing, the skills worth possessing, were changing. The Peerless had bought time for the world they’d left behind, but that was a trick that only paid out once; they couldn’t subcontract their own problems to a second group of travelers. Whatever talents they needed in order to survive in a state orthogonal to the history that had shaped them, they would need to master in just a year and half.

Yalda traveled up through the mountain again. The second-tier feed repairs were almost finished, the medicinal garden had been tidied and the damaged plot replanted. She met the chief agronomist, Lavinio, and they walked through the thriving wheat crop together. Having long ago grown accustomed to sunlessness, the plants appeared oblivious to their new state of endless flight.

Classes were being held throughout the Peerless now, within half a bell’s journey of everyone attending. Yalda sat in on one of Fatima’s, aimed at giving workers with a rudimentary education the kind of background needed to come to terms with rotational physics. Not everyone could end up as a researcher, but if the level of common knowledge throughout the community could be raised from mere arithmetic to four-space geometry, that higher base could only bring any future advances into easier reach—and if it brought them to the point where every gardener pulling weeds was also musing about the problems with Nereo’s theory of luxagens, all the better.

The teacher, Severa, posed a simple problem. “In an evenly ploughed field, a rope that is stretched from north to south crosses three furrows. The same rope stretched from east to west in the same field crosses four furrows. If the rope is stretched in the direction that allows it to cross as many furrows as possible… how many will that be?”

Diagrams blossomed on a dozen chests as the students sketched the scenario she’d described. Once they had the answer to this—and understood the reason it was true—half the secrets of light, time and motion would become second nature to them.

Back at the navigators’ post, Yalda met with her own student. She’d explained her plans to Nino when she’d informed him of his reprieve, but since then she’d been too busy to make good on her promise.

She sat on the floor, facing him. “Can you read the first dozen symbols?” she asked.

“Yes.” Nino’s tone made it clear that he took the question as an insult, but Yalda didn’t know how she could teach him if they weren’t clear about such things from the start.

“Can you form them? On your skin?”

Nino gazed back at her sullenly, offering her no clue as to whether she’d simply compounded her offense, or whether the answer this time was too humiliating to utter.

Yalda said, “This isn’t meant as some kind of punishment. I thought it might help you to pass the time, but if you want me to leave, I’ll leave.”

“As you wish,” he replied coldly.

Yalda was tempted. “Why treat me as if I’m your enemy?” she asked. “If I can accept that you had no malice toward us, can’t you return the favor?”

“You’re my jailer,” Nino said. “I make no complaint about my loss of freedom, but a jailer is not a friend.”

Yalda resisted the urge to launch into a tirade on his ingratitude. “I’d send you another teacher in my place if that would help, but I might find it hard to fill that position, and I’m not sure what the rest of the crew would think of it.”

“And what do they think of you coming here?” he asked.

“I haven’t made it widely known,” Yalda admitted. “But if I sent someone else, there’d be no end of talk about it.”

Nino shifted one leg across the floor. “What difference does it make to you, if I can read and write?”

Yalda said, “No one can survive with nothing but their own thoughts. If there were people willing to visit you, I’d be happy for them to come and lift your spirits as often as they wished. But whoever in the mountain once counted themselves as your friends, they’ve either changed their minds or they’re afraid to be seen to support you.”

“So you’ll teach me to read, then keep me quiet with your books?” He made it sound like a scheme for his subjugation, a conquest of his mind far more terrible than his physical confinement.

Yalda rubbed her face with her hands in frustration. “What would you prefer, then? I can’t just set you free.”

“So why are you trying to salve your conscience?” Nino demanded. “You have nothing to be ashamed of, for keeping me here.”

“No,” Yalda agreed, “but I will have if you lose your mind.”

“Why?” Nino wasn’t being sarcastic; he was genuinely puzzled. “Why wouldn’t the shame be mine alone?”

Was this a matter of pride for him? Of self-reliance? The last thing she wanted to do was undermine the resilience he already possessed.

Yalda said, “You did something foolish that could have killed us all—but while you’re alive on this rock, we still have the same duties to each other that apply to everyone else. Once I’ve ensured that the Peerless is safe from the risk that you might repeat your actions, everything else remains unchanged. Inasmuch as it’s practical, I still owe you meaningful work and the chance of an education—and you still owe me your participation. It gives me no pleasure that this obligation is so much harder to fulfill now, but that’s not enough for me to pretend that it has ceased to exist.”

Nino fell silent, but he looked less sure of his stance now. There was nothing degrading in being asked to pull his weight.

Yalda struggled to understand his position. He did not despise his captors; he would not have joined the crew without Acilio’s bribe, but he hadn’t come here poisoned with contempt for their ambitions. Acilio had rationalized away the risk of mass murder by implying that the same deaths were just a matter of time, but even if Nino was skeptical about the mission’s prospects, surely he gave the travelers some credit for good intentions.

“Where will it lead?” he asked. “If I learn what you want me to learn, what job could I end up doing?”

“That’s hard to say,” Yalda confessed. “But you can’t be a farmer anymore. You need to start with a simple education, and then find out what other aptitudes you have.”

Nino considered this, at length. Perhaps he was wary of raising his hopes too high. Yalda didn’t want to set him up for a fall, but a few modest steps that might eventually open up new possibilities for him had to be better than letting him rot here until he died.

“What you say makes sense,” he conceded. “If you’re willing to try to teach me, I’ll do my best to make it work.”

As the layer of burning sunstone came closer, the noise and heat from the engines became oppressive and the machinists and navigators prepared to move up to the second tier feeds. The Peerless had acquired so much momentum that a few days without manual corrections would make little difference to the course it was following, and any slight drift that occurred could easily be dealt with once the second tier fired up.

This would be a perfect opportunity to dispose of rubbish, Babila noted, looking around the bare cavern of the navigators’ post, now stripped of its benches and instruments. Anything we don’t want cluttering up the mountain, just leave it here to be blown into the void. Her gaze lingered on the door to the prison.

Clutter is just another word for wealth, Yalda replied. We’re not so rich that we can afford to throw anything away.

Frido had long ago stopped taking sides, at least openly. Help me check the release charges? he asked Babila; she followed him out of the room. Before igniting the second tier, they were going to set off explosions in the first-tier feed chambers to weaken the whole stub of rock that needed to be cast off.

Yalda opened the cell and led Nino out. For the first few steps he was disoriented, blinking and cowering at the strangeness of the vastly larger space, but he recovered his composure rapidly. Yalda knew better than to offer him solicitous words; they walked together in silence, through the empty feed chambers, out to the stairs.

“How much time has passed?” he shouted, as they began ascending. “Since we left?”

“Nearly half a year for us,” Yalda replied. The teacher in her wanted to conduct the conversation in writing, but Nino was walking ahead of her and he hadn’t yet mastered drawing anything on his back.

“And at home?”

“Almost as much. Let me think.” Yalda had not been keeping track of the old calendar; she had to calculate the answer on the spot. The only practical approach was to use the home world’s idea of simultaneity to link the two histories; the date obtained that way would cease advancing while the Peerless was traveling orthogonally, but was otherwise well-behaved. Attaching the definition of “now” to the Peerless’s own meandering history would have made the date back home race into the infinite future as they accelerated, swing back all the way to the infinite past as they reversed, and then return to sanity just in time for the reunion.

“About ten days less,” she said.

“I see.” Nino looked away across the stairwell, pondering something.

“Why?”

“Maybe I’ll have grandchildren soon,” he said.

“Oh.” Yalda wasn’t sure if he expected congratulations.

“I forbade it until my children had two years more than a dozen,” he explained. “I’m hoping that they’ll wait a few years longer, but it’s hard to know what they’ll choose.”

“I’m sure they’ll be sensible,” Yalda offered, without much conviction. “So what did you tell them, about joining the Peerless?”

“I said Eusebio was in such desperate need of farmers that he was willing to pay my family to have use of my skills.”

“How did they take that?”

Nino paused on the stairs. “They wanted to come too. I told them it was too dangerous for all of us.”

The noise of the engines gradually receded. However disturbing it was to contemplate the prospect of weightlessness, Yalda had decided that it would be worth almost anything to be rid of the endless hammering of flame on rock.

“Are your brother’s children older or younger?” she asked Nino.

“Younger.”

“So do you think he’ll put pressure on his nieces and nephews?”

“No,” Nino replied. “That’s not his way. I’m more worried that they might have trouble controlling themselves.”

At the top of the second tier they left the stairs. The only way to reach the new navigators’ post was through the feed chambers, and these ones would not be empty.

“Put your hands behind your back,” Yalda insisted. “For appearances’ sake.”

Nino complied; she pressed them together, then wrapped one of her own, larger hands around them. She would never have actually used melding resin, but it couldn’t hurt that anyone who saw them would be unable to tell at a glance that her prisoner was in fact topologically free.

They crossed the outermost chamber unseen, but in the next, Delfina was at her post inspecting the tape writer. “You’re letting that murderer walk through here?” she shouted at Yalda, incredulous.

“There’s no other route to his cell,” Yalda replied. The machinists had just spent days cleaning and testing their shiny new feeds; in the circumstances she could understand why anyone would feel affronted by Nino’s presence. But she’d had no choice.

Delfina approached them. “I can’t accept this!” she told Yalda angrily. “When Eusebio appointed you leader, do you think he intended you to put the life of one traitor above all of our own?”

Yalda had learned not to waste time taking issue with hyperbole like this. “I’m glad you’re here,” she said. “I wanted another guard to help watch over the prisoner as I escorted him to the new cell, but Babila and Frido were busy with the release charges.”

Delfina hesitated, but refusing the request would have been tantamount to conceding that Nino already posed no risk.

“If you could walk ahead of us,” Yalda suggested, “ready to block him if he tries to break free…?”

They threaded their way in silence through the banks of pristine clockwork, then into the next chamber. Onesta was inspecting the valves at the base of the liberator tank, but when she saw Delfina leading the procession she simply nodded in greeting.

In the navigators’ post, Delfina stood and waited until Nino was locked in his cell.

“I appreciate your help,” Yalda said.

“It shouldn’t have been necessary,” Delfina replied. “There shouldn’t have been a prisoner to move.”

“Nonetheless, I’m grateful,” Yalda insisted.

“That’s not the point.”

“Don’t forget the transition drill,” Yalda reminded her. “That’s the day after tomorrow.”

Delfina gave up. When she’d left, Yalda checked in on Nino. “Are you going to be—”

“Comfortable?” he suggested. “It’s identical to the last one.”

Yalda said, “If there’s anything in particular that you want, now might be the chance for me to sneak it in.”

“In the sagas,” Nino mused, “the rulers who survived were the ones who identified their enemies in time, and disposed of them swiftly.”

“I’ll be sure to keep that in mind.” Yalda began to leave, but then she stopped and turned back to him. “You learned the sagas?”

“Of course.”

“You’ve memorized them?”

“My father taught them to me,” Nino replied. “I can recite them all, word for word.”

Yalda said, “How would you feel about putting them on paper?”

Nino was bemused. “Why?”

“It would be good to have them, for the library.” In fact, she suspected that the library had a copy already. But every family passed down its own version, and perhaps in the future someone would want to ponder the nature of that variation. “If I bring you dye and paper, would you be willing to make a start on it? See how it goes?” Nino’s written vocabulary might not yet be up to the task, but any problems he struck would give them something to address in their lessons.

Nino considered it. They both knew this would be a kind of make-work compared to tending the wheat fields, but if he wasn’t yet sick of the uninspired calligraphic exercises Yalda had been setting for him, she was sick of thinking them up.

“All right,” he agreed.

Yalda was relieved. “I’ll get the supplies for you, before Frido and Babila arrive.”

“I taught the sagas to my sons, a few years ago,” Nino said. “After I’d done that, I thought I wouldn’t need them—I thought I’d just forget them.”

“But you didn’t forget them?”

“No.”

Yalda said, “I’ll bring you everything you’ll need.”

The new engines started up without mishap, blasting the stub of rock remaining at the top of the first tier away into the void. As Frido and Babila cheered, Yalda imagined herself congratulating Eusebio on the success of his design. Lately she’d found herself thinking about the return of the Peerless as if she’d be there in person—but then, she’d pictured Tullia walking beside her in Zeugma often enough; was it any more absurd to have the same kind of thoughts when she played the ghost herself?

Nino filled page after page with his transcripts. Yalda visited him to read these first drafts and suggest corrections—but only when one of her fellow navigators was sleeping and the other was out at the rim making observations. No one was being deceived, but she could still avoid provoking them with reminders of her contentious decision. The astronomers at the summit had found no obstacles ahead, but ensuring that the Peerless remained on course was still more than enough to keep everyone around her, machinists and navigators alike, far too busy to want to organize an insurrection if there was nothing forcing their hand.

When the Peerless reached the halfway mark of its acceleration phase, matching the speed of blue light, Yalda traveled up the mountain to speak to Severa’s class.

They met in one of the observation chambers. The students fell silent as they entered; they’d been told what to expect, but Yalda could understand how daunting it must be to see every star they’d grown up with—every subtle, distinctive smudge of light, every Sitha, Tharak, Zento or Juhla—raked into streaks of color more like a barrage of Hurtlers than anything else.

That was the view that first confronted them: looking straight out from the side of the mountain, where the small, haphazard motions of the stars were overwhelmed by the velocity of the Peerless. The speed of the mountain’s ascent was enough to align every color trail vertically, making a field of parallel furrows in the sky. The trails began and ended at disparate points, but all of them spanned about half a right angle, with red at the top and violet at the bottom. In this history made visible, the most recent report in violet always showed the star lower in the sky than the tardy red version.

Looking up toward the zenith, though, shattered any expectation that this pattern would merely repeat itself into the distance. Here, the stars’ own sideways motion could compete with the rocket’s forward rush, complicating the geometry enough to keep the trails from converging on any perfect vanishing point. More surprisingly, many of the trails here were completely inverted compared to the norm, their red ends poking down—and both kinds of trail faded out before traversing the full spectrum, the red-tailed never getting past green, the violet-tailed barely reaching indigo. On top of all this, the upper part of the sky was simply more crowded than the lower, giving the bizarre impression that the stars the Peerless was approaching had somehow receded into the distance, clumping together like the buildings of a town you were leaving behind.

Yalda addressed the students. “I know this looks strange to you, but we’re here to make sense of it. Everything you’re seeing here can be explained with some simple geometry.”

Severa had earlier had the class construct two props for the occasion. Yalda took them from her and set them down on the floor of the chamber. “To start with, I’d like you to examine these objects, please, and draw them as they appear side-on.”

The props were octagonal pyramids made of paper, one with a fairly shallow pitch and the other much steeper, mounted on simple wooden stands. The students gathered around them and squatted down to obtain views square with the base.