This science fiction classic became a paradigm for many sf plots to follow. An interstellar ship drifting aimlessly through space is peopled by inhabitants who have forgotten its history. The ship is their universe as they farm, raise families, and battle the mutants that inhabit the ship's upper levels. Can young Hugh Hoyland unravel the ship's mysteries and convince its inhabitants of his discoveries? Heinlein adroitly explores issues of morality and the folly of blind loyalty while delivering an action-packed story full of believable characters.