On the first day of Sara's appointment as Magistra Descendant to the Assembly of Terravine, Public Works decided they needed grassroots support for the plant.

"I mean, I agree in principle," Sara had tried telling him, as he gestured at his hand-annotated wallcharts. "But for one thing, I'm supposed to be neutral, and for another thing, people might be eating!"

"You see, Magistra Lobo, that's just the sort of avoidant attitude we're trying to eradicate," said Public Works. "Knocking on doors, that'll do it."

The man did actually have a name, Sara thought, while he was talking her into it. It might be Smith or Singh or Park. Light would know.

"It's Nguyen," Light told her.

"I knew it." Sara knocked on the first door they came to and had a moment of dissonance: sometime in the last ten years, she'd stopped recognising everyone in the colony. "Excuse me, citizen. My name is Sara Lobo. Could I have a moment of your time?"

The woman looked at her with narrowed eyes. "Are you here to bang on about cultural ties and the longitudinal view of history? And the importance of holding onto our shipboard and Earthbound past?"

"No," Sara said. "That's the Magistra Ancestral. I'm here to talk about sewage."

On day two, Sara was confirmed in her appointment, the department made a formal proposal to the Assembly, and Light fell out of a tree.

"It's really the ideal site," Public Works was saying to the gathered members. "It's a reasonable distance from clean water sources but it also has a decent height of inflow."

"I see," said the Archon, in tones that suggested she really didn't.

"All this time we've been getting by with bits and pieces of technology scavenged from the ship! And not even scavenged with thought, or put to use efficiently! Did we really spend generations crossing the gulfs of interstellar space just to dig ourselves giant latrines?"

"No?" said the Magistra Ancestral, after a minute of silence suggested this had not been a rhetorical question.

"And the worst part is this!" he said. "Thirty years ago when we surveyed the place from orbit we just didn't consider the requirements of terrestrial waste treatment."

"I see," the Archon said, again, and Sara imagined Public Works standing there on the bridge as the ship made landfall, pointing at an annotated wallchart.

"If you'll let me show you the plans, honoured Archon," he went on, and suddenly the air above the table contained a revolving three-dimensional blueprint. "See, here's road access. Here are the sandbanks, for the gravel we'll need. Here's the way down to the sea. And, er, this building here—Magistra Lobo, I think that's—"

"It's my house," Sara said, and then looked up: someone was trying to get her attention from the doorway. "I'm sorry, Mr Nguyen, I have to go," she said, reading the scribbled message. "My partner has had an accident."

After three decades in part-occupation of a human body, Light had not become resigned to its frailties.

"Let me guess," Sara said, "you went chasing after a missing cat, got five metres off the ground and then forgot you had a body. Right?"

She closed the door and dimmed the floor illumination, so Light's head hurt a little less.

"That is—ah." Light closed its eyes. "Perspicacious."

"The cat's in the kitchen drinking the hypoallergenic nutritional supplement that Nanni Julia won't touch because it tastes like pants. The rest was pretty easy to figure out."

"You—" Light propped itself on its elbows with some difficulty, "—are busy, and you must take care of Julia. . . ."

"Shut up, Light. I've spent my entire day chasing after Nanni Julia and the Department of Public Works. I'd rather look after you. Go to sleep."

Light did, and woke up a short time later still feeling like it, as though there were nothing between its body and the chrome and gunmetal sky. A hoarse voice was calling for something to drink. Light pulled one of Sara's cardigans around its shoulders and took some water through to Nanni Julia, but Nanni Julia threw the glass at its face and Light retreated into the open space of the house.

Sara turned at the movement. "Did she—" She made a precise gesture.

"Yes," Light said.

"I'm sorry." Sara waved a hand and the schematics in front of her, reversed from Light's perspective, blinked out of the air. "Light, I don't know why they've got me looking at these things. I don't want to be Magistra Descendant! I don't want to keep a weather eye out for the colony's future. What I want is for them not to be building a sewage works outside my house. And for Nanni Julia to stop throwing things at you. Is that so terribly unreasonable?"

"No." Light was shivering, the sea mist creeping through the gaps in the shutters. "But you could have declined the appointment."

"Eh," Sara said, waving her hand again, "who's ever done that, in the brave new Assembly of Terravine. Come on, back to bed with you, you've had a rough day."

Light woke up in the morning feeling more like herself. She made breakfast for Nanni Julia, who said something rude in Konkani; she fed the cat and returned it to its grateful owner; and then she sat down to consider the blueprints.

"I can assist," Light told Nguyen, on day five. "I'm afraid I have no recent qualifications in the field. But I was intimately acquainted with the process of human waste reclamation for more than two hundred years."

"Et tu, darling Brute," Sara said, but Public Works grinned and gave her a handful of explanatory pamphlets.

Day eleven was week's end, and Nanni Julia was well enough to go to mass, but wouldn't sit next to Light. "It's not right," she hissed, "something like you in a place like this"—and Sara rolled her eyes, but Light didn't mind. That morning, Nanni Julia had called Sara by her mother's name; Light hadn't heard it spoken in decades. She got up quietly and went to sit at the back.

After the service, which centred on themes of growth and renewal, Sara got a determined look on her face and went up to take communion. Light was distracted by a little girl catching at her sleeve.

"Excuse me," she said, "but are you really—it? Her?"

"Both will do," Light said.

"But you're the ship," the little girl persisted.

"Yes," Light said, looking up though the skylight. The ship itself—and Light had taken a long time to reach this place, where she could think in two separate parts of the ship itself and she, herself—was in geostationary orbit above Terravine. Light could feel its passage through space, its weight and tether. "I am the Earth generation ship Light, like a candle flame, last of the last."

"Why were you called that?" the little girl asked.

"There was a poem written about me before the journey," Light said. "Light / like a candle flame / carried out to the stars. It was thought appropriate, and it advanced no religion, no political position. Who knew what you would be, or become, after seven generations? The poet was a child from Wichita, Kansas."

Who had not been chosen in the ship lottery, Light recalled: who had lived and died in Wichita, Kansas, her body boneless beneath the choking dust.

"What do you do now you're a person?" the little girl asked.

"I was always a person," Light said. But paying rent in two places these days, as Sara had once described it. A piece of a ship's consciousness in a human skin, with that great remainder still out in orbit, rocked by solar wind.

"I mean, now you don't have to go anywhere?"

"I find lost things," Light said. "And I build new things."

"That sounds okay," the girl said, and Light smiled at her before turning away.

Sara was moving across the room, her footsteps ringing on the sunlit floor. "I was right," she said. "A certain person who shall remain nameless—"

"Nguyen. His name is Nguyen."

"—has already delivered unto Father Ignatius his own little homily about growth, renewal and waste processing. Even if I do agree in principle—"

"Do you agree in principle?"

Sara groaned. "I look to Terravine's future welfare. I'm supposed to be independent of day-to-day concerns."

Light nodded.

"But what with you and the blueprints, and Public Works and the pamphlets, and now my priest and my grandmother telling me all about how cleanliness is next to godliness, I'm starting to wonder if the Magistra Ancestral's work follows her home. Or to church."

"I'm sorry it's so trying," Light said, and Sara sighed and put an arm around Light's shoulders.

"Are you all right?" she asked. "Before, with the little girl—you seemed upset."

"I'm fine," Light said.

Sara committed to the cause on day nineteen, when a citizen made the mistake of putting their hands on their hips and saying: "How much shitting can one colony of four thousand people do?"

"Frankly, sir, I think you alone contain quite enough—"

"Thank you for your time," Light said. "For statistical information, please don't hesitate to contact the Department of Public Works."

"But in the meantime," Sara said, "if you want your community's water supply contaminated with disease just because you can't get your head out of your—"

"Sara."

"—long enough to see that a little construction work and a spoilt view are a small price to pay for—"

The door slammed.

"Sewage disposal is necessary for a long-term sustainable future," Sara said, her hands on her hips. "Do either of you have anything you wish to say?"

Light shook her head, and Public Works just looked delighted. "You read the pamphlets!" he said, and they marched on.

"Light," Sara said, late that night, after Nanni Julia had gone to bed and she and Light were sitting on the curve of the dunes, the tide creeping purplish and bioluminescent below. "Did you have to deal with things like this, before? When you were—what you used to be."

"What I am." Light held a hand up to the sky, occluding the fine dusting of stars. The last observers had been able to see that from Earth, Sara remembered: the same spiral arm, the same galactic neighbourhood.

"No," Light said. "There were no meetings, no petitions. Only survival."

As Sara watched, a bright pinprick described a curve across the darkness, and seemed to pause and revolve against the familiar backdrop. "What's that?"

"That is a salvage detail," Light murmured. "They are searching for aluminium and titanium. To take such things from beneath the ground would take great heat and pressure, and they can be reclaimed from my hull."

Sara shuddered. "I hope they really need them. I hope they're not making toe rings or saucepans out of them."

She meant it as a joke, but Light's eyes were steady on her, blank as smooth metal.

"Do you presume to speak to me, Magistra Lobo, of what is necessary? Of what must be kept, or left behind?"

She was shaking with anger, and then it seemed to drain from her, leaving her still and quiet. Sara waited another moment and then gathered Light in her arms, muttering into her hair, you're here, you're all right, as though it might assist, or mean anything.

"How can you be on his side?" another citizen yelled on day twenty-seven, having come to the door brandishing a petition of his own. Light had been complaining of a headache, which worried Sara after the tree incident, but she'd come along anyway.

"Mr Nguyen is an excellent engineer," Sara said primly. "And if you'd care to listen just for a moment to what he has to say—"

"I've heard the speech," the man said. "All about the need to prepare the colony for growth and expansion! Infrastructure and the bright new future! We came here to get away from that! We came here to live in harmony with the world around us!"

"That's true," Sara said, hesitantly. "But it's also true that we've been taking an amateurish approach to waste processing."

"You're the Magistra Descendant!" the man snapped. "Doesn't that mean you have to look after our descendants? You're supposed to stop us repeating all the old mistakes!"

"It's just a sewage works," Sara said, still hesitant. "And we need it. We're outgrowing the initial plumbing arrangements, which were only meant to be temporary in any case—"

"And what will we need next?" the man demanded. "And what will we need to mine, or strip, or destroy, to build it?"

"That's not how it works!" Sara said, falling wholly off-script. "One little sewage works isn't going to lead to—you know, to that! To anthropogenic climate change!"

"And who's going to stop it?" the man snapped. "You?"

He was staring past Sara and Nguyen at Light, who was inspecting her bitten fingernails.

"No," she said. She sounded exhausted and in pain. "Not me."

On day thirty-five, the pro-sewage-plant faction had three hundred and sixty-two signatures, to the anti-sewage-plant faction's three hundred and fifty-four.

"Too close," Sara told Nguyen. "It'll come to a vote in the Assembly. Cheer up! Pamphlets for everyone!"

He gave her a gloomy look before going up to the public gallery, and Sara took her seat at the table opposite the Magistra Ancestral. She was a quiet woman with a topknot of white hair. Far more befitting the post, Sara thought, appointment by random ballot notwithstanding.

"A full agenda for today," the Archon said. "The first order of business is a submission from the most recent ship detail. Dr. Desai, if you could, please."

She gestured at one of the other Assembly members, who stood up. "It's complicated," she said, sounding nervous, "and there will be a full report to the Assembly in due course, but in brief: this collection detail will be the last."

"Why is that?" asked the Archon.

"The ship is going dark," Dr. Desai said. "Most of the useful constitutive materials have been salvaged by this point, and it's been running with minimal energy consumption for ten years at least. It's a planned obsolescence," she added, hastily. "No one is saying that it hasn't been properly maintained or anything like that. But soon it won't be safe for our people to walk around there any longer. The computer core is intact but it no longer has complete connectivity to the outer shell."

"I see," the Archon said. "We'll await the full report. Thank you very much."

"Now, following a proposal in opposition and a counter-proposal from the Department of Public Works, the Magistra Descendant wishes to make the case for a sewage plant in Terravine, on the western shore."

Sara stood up, glanced above at Nguyen and at the notes in her hand, and then looked straight at the Archon. "One day I'll be superfluous to requirements," she said. "Seven generations from now we won't need a Magistra Descendant or Magistra Ancestral. We won't need reminding to look to our future or preserve our past. It'll be part of who we are.

"I was six years old when we made landfall. I remember what it was like, to be carried through space, and to know everything was provided for, everything was done. But we're here now. Shouting at each other on doorsteps, producing pamphlets, doing our best to avoid the old mistakes. If we call for help, no one will come. Time to grow up, don't you think? Time to shovel our own shit."

She sat down. Nguyen got up and provided some information on the technical specifics, answering the Assembly members' questions, and after that the representatives of the anti-sewage faction came down from the public gallery and spoke about the need for harmony with one's agrarian environment. Sara barely heard any of it over the litany in her head, repeating itself over and over: the ship is going dark.

"Light," a voice said, and Light paused in the doorway. "It's you."

"It's me," Light agreed. She waited, but Nanni Julia did not throw anything at her.

"No," Nanni Julia said. With difficulty, she rose from her rocking chair and walked slowly to the window. Light assessed whether she would require assistance, then stood still. "I mean, it's really you. Light, like a candle flame."

"Yes," Light said. People had sworn by her, once. Light, like a candle flame—when one pledged an oath one meant to keep, or dropped a hammer on one's toe. It used to make her uncomfortable.

"I don't like seeing you," Nanni Julia said, fretfully. "You were everything to me. Family, friend, teacher. You were the first thing in the morning and the last thing at night. And now I'm an old woman, and you—you look like that."

Light looked down at herself: at the faded tunic, at her bare feet in sandals. At the broken fingernails that Sara had tried to stop her from chewing, at the shape of the bones beneath her skin. "This is where we live now," she said, not knowing if it would be consolation.

"I'll be going soon enough," Nanni Julia said, matter-of-fact. "Off to my life everlasting, and all the flights of angels. Can I tell you a secret?"

"Of course."

"I'm not going anywhere," Nanni Julia said, her voice conspiratorial. "Put me in the hole when they dig it, I can be sewage. I can be the dirt that makes things grow. You brought me here and here I'll stay."

Light nodded, and went to join her at the window. "Shall I take you to mass in the morning?" she asked.

"You shouldn't," Nanni Julia said, again fretful. "You're not a Catholic."

"Perhaps not," Light said. "But I was conceived in sin."

Nanni Julia smiled. "You're a good girl, Light. You were always so good to us. Now I'd like to sleep."

Light helped her back to bed and fluffed the pillows. "Goodnight, ship," Nanni Julia said, as Light was on the threshold.

"Goodnight, Julia," Light murmured, and went out to Sara, who was waiting for her on the path through the dunes.

Sara waited until they were by the water's edge, the last of the day's light filtering greenish through the shallows.

"Were you going to tell me, Light?" she asked. "I suppose you weren't. You were just going to let me think you had a dizzy spell and fell out of a tree."

"I did," Light said. She sounded embarrassed. "I did."

"But it's because of that." Sara gestured upwards, to where the ship was visible as the first star of twilight.

"It was a planned obsolescence," Light said.

"I thought you wouldn't leave," Sara said. "You'd never leave us."

She was sounding like a child, she knew, and her mind was full of the last memories of childhood: the faint buzz of shipboard air recirculation and the voice who always answered, steady as the stars beyond the glass.

"I will stay as long as I can," Light said, and kissed her.

Sara whispered soft inarticulate things into her mouth, and held her. After a minute she wiped her eyes and said, "Light, they're building a sewage plant next to our house."

"I know," Light said. "You could have voted against."

"Like I could have declined the appointment? You're hilarious."

"I try," Light said. "We could move."

"There's a whole planet, I'm told," Sara agreed, kneeling down to trail her hands in the water. "But, you know what? I kind of like it here."

"So do I," Light said. She got down on her knees to join Sara, tide-phosphorescence gleaming at her fingertips. Sara imagined waking with Light in the early morning, reaching towards her through the wreathing mist.

"Well, then," she said, looking up into the sky. "I suppose we'll be here a little while yet."