The viability of the planet Inferno depends on the coexistence of two antagonistic human societies: the Spacers, who depend on robots for everything, and the Settlers, who eschew artificial intelligence. When authorities begin to suspect the existence of a rogue robot, created without the Three Laws that ensure subservience to humans, the delicate partnership begins to unravel. Based on a discussion with the late Asimov, Allen's ( Orphancy Creation , Baen Bks., dist by S. & S., 1988) latest work is a detective novel cum literary tribute that might have been written by the master himself. A good choice for large sf collections.