House of Stairs — William Sleator

Peter. Lola. Blossom. Abigail. Oliver. Five sixteen-year-old orphans. One by one, they are brought to a place that is unlike anything any of them has ever known. It's not a prison, not a hospital. It has no walls, no ceiling, no floor. Nothing but endless flights of stairs leading nowhere -- except back to the red machine. The five will learn to love the machine, will let it rule their lives. But will they let it kill their souls?