To my wife, Sandra

I must express my thanks to Larry Niven, David Brin and Eric Brown, who took the trouble to read and comment closely on drafts of this novel, and on the imagined universe it portrays: thanks to their input the quality of this work has been greatly enhanced. Thanks also to Arthur C. Clarke, Bob Shaw, Charles Sheffield, Joe Haldeman, and David Pringle for their words of praise and encouragement. Finally I owe a great debt of gratitude to Malcolm Edwards, my editor at Grafton, for his patience, encouragement, and close attention to the development of this work.

It was when the foundry imploded that Rees's curiosity about his world became unbearable.

The shift started normally enough with a thump on his cabin wall from the fist of Sheen, his shift supervisor. Groggily Rees pulled himself from his sleeping net and moved slowly about the jumbled cabin, grinding through his wake-up routines.

The water from the rusty spigot emerged reluctantly in the microgee conditions. The liquid was sour and cloudy. He forced down a few mouthfuls and splashed his face and hair. He wondered with a shudder how many human bodies this water had passed through since its first collection from a passing cloud; it had been dozens of shifts since the last supply tree from the Raft had called with fresh provisions, and the Belt's antique recycling system was showing its deficiencies.

He pulled on a stained, one-piece coverall. The garment was getting too short. At fifteen thousand shifts old he was dark, slim — and tall enough already and still growing, he thought gloomily. This observation made him think with a stab of sadness of his parents; it was just the sort of remark they might have made. His father, who had not long survived his mother, had died a few hundred shifts ago of circulatory problems and exhaustion. Suspended by one hand from the door frame Rees surveyed the little iron-walled cabin, recalling how cluttered it had seemed when he'd shared it with his parents.

He pushed such thoughts away and wriggled through the narrow door frame.

He blinked for a few seconds, dazzled by the shifting starlight… and hesitated. There was a faint scent on the air. A richness, like meat-sim. Something burning?

His cabin was connected to his neighbor's by a few yards of fraying rope and by lengths of rusty piping; he pulled himself a few feet along the rope and hung there, eyes raking the world around him for the source of the jarring scent.

The air of the Nebula was, as always, stained blood-red. A corner of his mind tried to measure that redness — was it deeper than last shift? — while his eyes flicked around the objects scattered through the Nebula above and below him. The clouds were like handfuls of grayish cloth sprinkled through miles of air. Stars fell among and through the clouds in a slow, endless rain that tumbled down to the Core. The light of the mile-wide spheres cast shifting shadows over the clouds, the scattered trees, the huge blurs that might be whales. Here and there he saw a tiny flash that marked the end of a star's brief existence.

How many stars were there?

As a child Rees had hovered among the cables, eyes wide, counting up to the limits of his knowledge and patience. Now he suspected that the stars were without number, that there were more stars than hairs on his head… or thoughts in his head, or words on his tongue. He raised his head and scoured a sky that was filled with stars. It was as if he were suspended in a great cloud of light; the star-spheres receded with distance into points of light, so that the sky itself was a curtain glowing red-yellow.

The burning scent called to him again, seeping through the thin air. He wrapped his toes in the cabin cable and released his hands; he let the spin of the Belt straighten his spine, and from this new viewpoint surveyed his home.

The Belt was a circle about eight hundred yards wide, a chain of battered dwellings and work places connected by ropes and tubes. At the center of the Belt was the mine itself, a cooled-down star kernel a hundred yards wide; lifting cables dangled from the Belt to the surface of the star kernel, scraping the rusty meniscus at a few feet per second.

Here and there, fixed to the walls and roofs of the Belt, were the massive, white-metal mouths of jets; every few minutes a puff of steam emerged from one of those throats and the Belt tugged imperceptibly faster at his heels, shaking off the slowing effects of air friction. He studied the ragged rim of the nearest jet; it was fixed to his neighbor's roof and showed signs of hasty cutting and welding. As usual his attention drifted off into random speculation. What vessel, or other device, had that jet come from? Who were the men who had cut it away? And why had they come here…?

Again the whiff of fire. He shook his head, trying to concentrate.

It was shift-change time, of course, and there were little knots of activity around most of the cabins in the Belt as workers, grimy and tired, made for their sleep nets — and, a quarter of the Belt's circumference from him, a haze of smoke hovered around the foundry. He saw men dive again and again into the grayish fog. When they reemerged they tugged limp, blackened forms.

Bodies?

With a soft cry he curled, grasped the rope and sprint-crawled over the diffuse gravity wells of cabin roofs and walls to the foundry.

He hesitated on the edge of the sphere of smoke. The stench of burnt meat-sim made his empty stomach twist. Two figures emerged from the haze, solidifying like figures in a dream. They carried an unrecognizable, bloodied bundle between them. Rees anchored himself and reached down to help them; he tried not to recoil as charred flesh peeled away in his hands.

The limp form was bundled in stained blankets and hauled tenderly away. One of the two rescuers straightened before Rees; white eyes shone out of a soot-smeared face. It took him a few seconds to recognize Sheen, his shift supervisor. The pull of her hot, blackened body was a distant tugging at his belly, and he was ashamed to find, even at a moment like this, his eyes tracking sweat droplets over her blood-smeared chest. "You're late," she said, her voice smoke-deep as a man's.

"I'm sorry. What's happened?"

"An implosion. What do you think?" Pushing scorched hair from her brow she turned and pointed into the stationary pall of smoke. Now Rees could make out the shape of the foundry within; its cubical form had buckled, as if crushed by a giant hand. "Two dead so far," Sheen said. "Damn it. That's the third collapse in the last hundred shifts. If only Gord built strong enough for this damn stupid universe, I wouldn't have to scrape my workmates off each other like so much spoiled meat-sim. Damn, damn."

"What shall I do?"

She turned and looked at him with annoyance; he felt a flush of embarrassment and fear climb in his cheeks. Her irritation seemed to soften a little. "Help us haul the rest out. Stick close to me and you'll be fine. Try to breathe through your nose, OK?"

And she turned and dived back into the spreading smoke. Rees hesitated for a single second, then hurried after her.

The bodies were cleared and allowed to drift away into the Nebula air, while the injured were collected by their families and gently bundled to waiting cabins. The fire in the foundry was doused and soon the smoke was dispersing. Gord, the Belt's chief engineer, crawled over the ruins. The engineer was a short, blond man; he shook his head miserably as he began the work of planning the rebuilding of the foundry. Rees saw how the relatives of the dead and injured regarded Gord with hatred as he went about his work. Surely the series of implosions could not be blamed on the engineer?