A science fiction story, oddly, and rather pleasantly told in the style of an English novel-of-manners. It purports to be a biography and its nameless narrator, an older man, first meets Andrew Melmoth at the home of Sir Charles and his daughter Mary, whom he later marries. Andrew is a young scientist, working on the behavior of rats, and he meets Margaret at the same time-so that the progress of these two love affairs, and the ideas and personalities they reveal, are shown through letters, Andrew's diary, etc. Andrew can only see people bevavioristically, as he sees animals; Margaret, also unsure, remote, is presently taken away from him by an opportunist, and she becomes insane. The physicist represents the point of view that is in favor of bomb tests, but Andrew suspects that the human race is doomed- by genetic changes from radiation, and that the wild rats are the coming race, developing a culture of their own. He withdraws further from people; spends his nights in the rat-haunted sewers of London with an old rat catcher; and finally vanishes in the sewers altogether.... As science fiction, the idea of a subsidiary species taking over the earth is not new, nor altogether convincing. But as a novel it is absorbing, intelligent, well-written, and the night scenes in the sewers are quite unnerving.