A British scientist is discovered to have been passing information to the Communists, then kills himself. Another scientist decides that they might have brainwashed him by a sensory deprivation technique, but he doesn't know if someone really can be convinced to act against their strongest feelings. So he agrees to be the subject in an experiment in which others will try to make him stop loving his wife.
Following the suicide of Professor Sharpey, a scientist involved in an experiment sponsored by the British space agency to test an individual's reaction when he is deprived of essential sense stimuli, military security officer Major Hall presents Calder, the director of the laboratory where Sharpey worked, with evidence that the dead man was a traitor. Hall then visits Sharpey's associate, Dr. Longman, at Oxford University to continue his investigation. Longman angrily defends his colleague and claims that the experiment was responsible for the alleged security violations and the events leading up to Sharpey's suicide. He contends that Sharpey, the experiment's primary subject, was not a traitor but was brainwashed to give away the secrets. Determined to prove his belief, Longman submits himself to the experiment, is immersed in a tank of warm water for several hours, and emerges in a state of nervous collapse. Dr. Tate, an associate, and Major Hall, to help Longman prove his theory, attempt to undermine Longman's love for his wife, Oonagh, by brainwashing him and tape recording the session. Only after the apparent failure of the experiment does Longman begin to show signs that the experiment actually succeeded. He is indifferent when Oonagh announces that she is pregnant; their relationship becomes progressively uneasy; and Longman becomes infatuated with Annabelle, a "college widow." Major Hall becomes concerned over Longman's behavior and vainly attempts to undo the damage by playing for Longman the recording he and Tate made of the brainwashing session; but Longman remains unaffected and departs with Annabelle for her houseboat. Oonagh, in the last month of her pregnancy, takes a fall and begins labor; and the birth of his child brings Longman back to his senses.
