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.