When the end did come, there was some warning: a siren that wailed, for a few seconds.

At the time Yuri had no idea what it meant; he paid no attention to the sporadic briefings on shipboard events. He was on another punishment duty, scooping out muck from the interstices of a mesh floor partition, a grimy, demeaning job that you had to do on your hands and knees, working with a little cleanser the size of a toothbrush and a handheld vacuum hose. A make-work job a machine could have done in a fraction of the time.

Then the gravity failed.

It felt like the whole hull had suddenly dropped, like an elevator car whose cable had broken. Yuri found himself drifting up in the air, the little brush and the vacuum cleaner and his sack of dirt floating up around him. It was an extraordinary feeling, a mix of existential shock and a punch to the gut.

The Peacekeeper supervising him, a fat man called Mattock, threw up, and the chunky vomit sprayed over Yuri’s back and drifted up into the air, a stinking, noxious, stringy cloud.

Yuri knew what had happened, of course. After three and a half years of a steady one-gravity thrust, save for a brief turnaround at the journey’s mid-point, the crew had shut down the drive. During the cruise you could have forgotten you were in a starship, for long periods. Now here was the reality of the situation suddenly intruding. His latest prison really was a battered tin can light years from Earth.

And then, not five seconds after the acceleration cut out, the riot started.

It erupted all at once, along the length of the hull. The yelling was the first thing Yuri noticed, shouted commands, whoops, screams of defiance and fear.

The big fluorescent light fittings were put out immediately. The crimson emergency lighting system soon came on, shining from behind toughened glass, but the hull was plunged into a flickering, shadowy half-light. And people moved through the shadows, grabbing handrails and slamming at the partition flooring with booted feet, so that broken panels started hailing down through the crowded air. Others used whatever tools they had to hand, spanners, broom handles, they even wrenched rails off the wall, to smash up equipment.

The Peacekeepers were an early target too. Near Yuri, from nowhere, three, four, five people, men and women, came hurtling out of the air like missiles and slammed straight into Mattock. Struggling, his head surrounded by a mist of vomit and blood, the Peacekeeper had no chance of reaching his weapons. He looked to Yuri, who was clinging to the wall. ‘Help me, you bastard—’ A booted foot slammed into his mouth, silencing him.

Yuri turned away. He pulled himself around the walls, working his way across rails and equipment banks, trying to keep out of trouble, trying not to be noticed. He had a rendezvous of his own to make.

As he moved he observed that the hull’s population was split. Maybe a third of them were working in a coordinated way, savaging the Peacekeepers and, he saw, one or two astronaut crew members they’d got hold of, or systematically wrecking the internal equipment. Obviously they’d planned this, coordinated it for the onset of zero gravity. Most of the rest, scared, nauseous, were swarming around trying to keep out of the way of the violence. They were almost all adults, of course; the few kids, two- or three-year-olds born during the voyage, clung to their mothers in terror.

And up at the top of the hull Yuri saw a party gathering around the central fireman’s pole, preparing to climb up to the hull’s apex, up to the bridge. A woman he recognised, called Delga, was at their head. That was no surprise. He’d known her on Mars, where they’d called her the snow queen of Eden. On the ship she had quickly built a power base in the early days when, without alcohol, drugs, tobacco, the whole hulk had been like a huge rehab facility as everybody worked through cold turkey of one kind or another – and Delga, who somehow got her hands on various narcotics, had acquired a lot of customers. Yuri had kept out of her way on Mars, and on the ship, and he did so now. He dropped his head and concentrated on his own progress.

He got to his meeting point. It was just a kind of alcove on a central deck, a warren of thick pipes and ducts and power cables between two hefty air-scrubbing boxes. But it was tucked out of the way of trouble. He and his buddies hadn’t anticipated this scenario exactly, but they’d made contingency plans to meet here, in case.

And now, here he found Lemmy, and Anna Vigil, and Cole, nearly four years old, a timid little boy who clung to his mother’s legs, all waiting for him.

Wordlessly Yuri backed into the space, opened a maintenance panel on one of the scrubber boxes, took out a wrench and a screwdriver, and thus armed wedged himself in position before the others. After three and a half years he had a reputation on this hull. A loner he might be but he’d fight back, and was best left alone if there were easier targets. This had been the plan they’d cooked up, the three of them, when they’d thought ahead to bad times; this was the best Yuri could think of to protect them.

He heard a scream. In the shadowy chaos, he saw that three men had got hold of a woman. Yuri knew them all; he’d thought one of the men at least was a friend of the woman, who’d paired off with another guy. Yuri knew the woman too; called Abbey Brandenstein, she was an ex-cop and she could look after herself, but she was being overwhelmed. Now they were dragging her into a corner, though she was still fighting back. As the screaming got worse Anna Vigil covered little Cole’s eyes and ears, and hugged him close.

The noise was still ferocious, a clamour of yells and screams. More alarm sirens were sounding off, adding to the racket. There was no sign yet of the Peacekeepers taking any kind of coordinated action. Yuri saw Gustave Klein on the other side of the hull, flanked by a couple of his heavies, watching the action with a grin on his face. Maybe it was Klein who was really in control.

Lemmy peered cautiously up into the apex of the hull. ‘Delga’s reached the bridge, it looks like.’

‘What do you think they want?’

Lemmy shrugged. ‘To take the ship. Force the astronauts to whiz us all back to Earth. I bet there’s a similar breakout going on in the other hull; they’ll have timed it. I guess it’s the last chance we’ll get. There’ll be no hope once we’re on the ground, on a planet of Proxima.’

‘But they could smash up the ship before they win that argument.’

‘True.’

‘You think it’s going to work?’

Lemmy grinned. ‘Nah. Look.’ He pointed to the far wall of the hull.

An airlock hatch opened and a dozen astronauts tumbled out of the lock and into the hull’s cluttered spaces. They wore hard, carapace-like pressure suits of brilliant white, marked with arm stripes in gaudy recognition colours, red, blue, green. They had their helmets sealed, their faces hidden behind golden visors, and their movements were jerky, too rapid, over-definite – a product of military-class enhancements, Yuri had learned, exoskeletons, drugs, boosters from the cellular level up. They carried weapons of some kind, not guns, not in a pressure hull, but what might be tasers, even whips.

Some of the rebelling inmates went for them immediately. The astronauts fought back with clean, hard moves, and snaps of their tasers, rasps of the whips. They were like insects with their superfast movements and hard outer shells, like space-monster cockroaches in this chaotic human environment. Before them the inmates looked grubby and unevolved. People fell back howling, blood spraying into the air.

Meanwhile one group of astronauts, three, four of them, broke away and made for a big locked control panel a couple of decks higher up towards the bridge. More rebels tried to get in their way, but the astronauts were too fast, too definite, and their opponents were brushed aside. The astronauts unlocked the panel with brisk taps of gloved fingers, and plugged pull-out leads into sockets in their suits, perhaps for identity verification.