A rich, sweeping novel about first contact between humanity and another sentient species. From a star called the Mote, an alien ship ventures into the Empires of Man, but its pilot is accidentally killed before the races can meet. The Empire responds with a mission to the Mote -- one ship carrying civilian scientists, the other bristling with weapons; the Empire teeters between thirst for knowledge and fear of the unknown. The civilization of the Mote inhabitants presents endless riddles, despite the Moties' apparent candor. Slowly the pieces fall together; Moties have several physically differentiated castes; Moties have different sexes at different phases of life; Moties, trapped in their system by lack of faster than light travel, have undergone endless cycles of social collapse followed by renaissance. But it is almost too late before humanity learns the true danger posed by these beings so alien in mind and, more important as it turns out, body. If the human characterizations were as original as the Moties, this would be a great science fiction novel. As it is, it's very good indeed. A potential prize winner.