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Following the death of a fellow scientist accused of being a communist spy, Dr. Henry Longman (Dirk Bogarde) works to prove that his colleague had been brainwashed. To do so, Longman subjects himself to experiments in a sensory deprivation tank. This starts to take a heavy toll on his mental health; in particular, it alienates him from his wife. Additionally, his scientific credibility suffers and with it the chances for discovering the truth about his colleague. Wikipedia