“Seriously,” Xiaodan says. “I don’t know how much longer you’re keeping me down here, but –” He shrugs helplessly. “There must be some way I can pay you back. You or anybody else who’s helped me settle in. I want to.”

For a moment he can almost feel Sain watching him in the darkness, and he wonders what her expression might be.

“No promises,” she says at last. “But I’ll ask around.”

As it turns out there’s quite a lot Xiaodan can do, even with his fledging mental map of the city and no echolocation ability.

“This is just going to be manual labour.” Sain stops, with one of those pregnant pauses Xiaodan has learned to read by now. She’s wary there might be something he’s not telling her. “Fetching and carrying. Understand? They’ll be –”

“It’s fine,” Xiaodan says. “As long as they know I’m a bit slow.”

“He admitted it.” Sain’s trying not to laugh. Xiaodan hears her footsteps as she spins, talking to the empty air, then back to him. “No taking it back – no, seriously, they won’t mind. There’s plenty of other people in the same boat. So you’re sure?”

“I’m sure,” Xiaodan says.

After two days he’s not quite so sure.

People who can’t find their way around and can’t use echolocation typically do the simplest jobs. This means trudging, one after the other, in a long, long line snaking its way through the streets. They carry the heaviest loads everyone else would rather not deal with, given the choice.

Xiaodan carries building materials, hods full of roof tiles, jumping around in a discordant rhythm as he walks; he shoulders great baskets full of dung, which keep leaking thin, greasy trails all over his clothes and draw clouds of flies; he hoists bags of bone meal, compost and fertiliser, the smell of which leaves his nose streaming.

It’s not all tedium and frustration. The porters are friendly enough, and seem to understand Xiaodan’s not in the mood for awkward questions. As the clock chimes for their mealtime, and his colleagues sit down to eat, Xiaodan listens, and their conversations flesh out this curious little kingdom a bit further.

Maintaining the city seems to be a never-ending battle, and while the porters put a brave face on it, Xiaodan gets the impression a lot of them feel they’re losing. Slowly, yes, but losing even so. Some things they don’t lack for, but others are used up or worn out faster than anyone can replace them.

“Rotten wood…” begins one old man with several missing teeth, by the sound of it, and a voice as if he’s drunk a flagon of glue.

“Still good,” his friends finish, with a weary bark of laughter.

There are no trees down here, but they do grow other things, after a fashion. Xiaodan discovers, following the porters, that the city has an inner and an outer wall, and farmers tending their crops in the space between.

While there are no lightstones in the heart of the city, it turns out there are some still in the ground, dotted around the outer ring. Whatever the glow they give off, it’s close enough to actual sunlight that plants will flourish if left exposed to it.

“Looks funny, so they tell me,” one woman says, a softly spoken giant with a broken nose and a giant mop of hair. She holds up an ear of corn so pale it might have been bleached. “But it tastes all right. Makes flour that bakes like flour. Can’t ask for much more.”

Nobody else seems to think of the orange glow as anything other than a useful resource that shows no signs of running out. The woman – Fan Yan, she tells him – is one of the blind, and can’t even see it. She’s merely trusting that it’s there, given the effects.

The farmers’ jobs are difficult enough to begin with. You can hear the salamanders go past from the outer wall, apparently, and they’ve been known to charge it, left to their own devices.

“So what do you do?” Xiaodan asks.

“Burn fires just outside,” Fan Yan says cheerfully. “All that dung you’ve been humping around? Most of that is theirs to start with. They don’t like the smoke any more than we do.”

“I should go,” Xiaodan says, seeing the foreman waving through the gloom, from across the field. He looks wistfully at the lightstone, uncomfortably aware that without the medicine he took, they’d probably have to drag him away.

“Give Sain my regards.” Fan Yan places her hands together and does a surprisingly genteel bow.

“How do you –?” Xiaodan begins. He digs a knuckle into his forehead, grimaces, then looks up. “Who is she –?”

Sain sounded, of all things, disappointed. Why? What was she expecting?

“Everyone knows who took you in.” The tall woman laughs. “But if she hasn’t told you the whole story, then I’m not going to spoil anything. No! Go on. Get.” She waves him off. “Back to work.”

While people are plainly grateful for Xiaodan’s assistance, and the errands keep coming, there are certain things nobody wants him to go near. Hanging around the kitchens is one thing, but at one point he hears another line stamping past his own carrying sloshing buckets brim full of water, and asks who gets that duty.

“Not you,” says the man just ahead, not unkindly. “No offence meant. Not when you’re still this new. You seem like a nice lad to me, but there’s limits, right?”

“Right,” Xiaodan murmurs, and shifts the load across his shoulders.

There are some concessions. A counterweight, for the engineer currently working a shift up the clock tower; not something he expected to be entrusted with, but it’s not far from the square where the children spend mid-day, and Xiaodan manages the trip in half the time it took him two days before.

He climbs the spiral stairs around the wall of the tower, slow and steady, and only falters once, when several bats come fluttering down to find out what this intruder thinks he’s doing.

“Are you okay?” A voice, from higher up the stairs, stifling laughter.

“I think –” Xiaodan swings his free arm frantically. “They won’t – there.” The bats retreat, cheeping indignantly. He can hear them flitting back and forth through the darkness. “Persistent, aren’t they?”

“You get used to the company,” the voice says. “After a day or two. Sounds like you’re clear. Come on up.”

The engineer is named Han Ping, an affable young man two years Xiaodan’s senior. As well as keeping the timepiece itself – a mighty water-clock – in working order, he has the responsibility of standing lookout. This usually falls to people who can see, at least a little, though apparently it’s more about listening for danger.

“Salamanders,” Han Ping says solemnly. “Floods. They had two, a long time ago. First one washed half the lower level away. Nothing for you to worry about, mind.”

The two of them are sitting on the parapet, gazing out into the void.

“Why do you say that?” Xiaodan asks. He looks up, trying to count the lightstones overhead. The faintest of these tiny orange stars are almost imperceptible.

“You’re not staying,” the engineer points out.

How has this become public knowledge? Is Sain going around telling everyone she runs into, or did somebody who heard about his orientation pass it on?

“Not that I’d blame you,” the other man continues. “If you really walked in here without meaning to. It’s a hard life, that’s for sure.”

“But you’re okay with that?” Xiaodan says.

“I know what the empire’s like.” Han Ping kicks his heels against the stones. “Heard enough about that to convince me I’m better off down here. Maybe I’ll take a look, some day, but… not yet.”

“The Shen Dynasty died off two hundred and fifty years ago,” Xiaodan mumbles. He feels the sudden urge to point out how fantastical, how illogical, all of this comes across. “There’s been four more since –”

“What?” Han Ping says. “Oh. I guess. Is it really that different, though? People like to think so, but…” He trails off. “Time makes fools of us all, right?”

Who were the Zhǎiguān army, to think they actually stood a chance? An invasion?

“It does,” Xiaodan says quietly, and for the first time he wonders how, exactly, the Mùrén government or the invaders would view this secluded pocket of religious independence. Or the Yèkǒng, come to that. Do they hate all of humanity without exception?

He’s still mulling everything over later that day when Sain comes to his room, to ask him if he’s hungry. Lost in thought, leaning back in his chair, Xiaodan doesn’t even realise she’s there until he feels the sensation of something hollow deposited over his head. One of her larger bowls, thankfully empty.

“I said –” Sain rests her hand on top of the bowl, rocking it back and forth. He can feel the rim lightly digging into his ears.

“I was thinking.” He turns, pushes her away, and lifts the bowl off his head.

“I thought I could smell smoke.” She crouches down. From the way her breathing changes, Xiaodan can tell she’s squatting on her haunches. “What about?”

“I want –” This is harder than he was expecting. He doesn’t want to disappoint her. At the same time, he wants her to listen and say yes, just like that.

Apparently he’s changed precious little in nine years.

“You want,” Sain says gently, as if she can sense he’s struggling.

“I want –” Xiaodan takes a deep breath. “I want something more. Than fetching and carrying.”

“We talked about this,” Sain says slowly. “People need fetching and carrying. It’s nothing to be ashamed of, if you can’t do –”

“With all due respect,” Xiaodan interrupts. He hopes fervently this isn’t coming off as high-handed as it sounds in his head. “I understand what you’re getting at, but… I don’t think you really know what it is I can or can’t do.”