Spence Olham is a scientist working on a top-secret government projectwho must discover the identity of a humanoid robot who has infiltrated the project's facility and taken the place of a worker there. He is accused of being an android himself and must both clear his name and reveal the identity of the traitor. Knowing that there is a self-destruct mechanism in the robot but not what it is, Olham is set on a psychological goose chase which culminates in an unexpected ending. It is one of the first stories Dick wrote which explores a common theme inhis science fiction, the question of what is human.