A "psychopsychiatrist" played by William Hurt takes his experiments in a sensory deprivation tank to the extreme and regresses into a primitive state. Is this a cutting-edge depiction of the inner evolutionary state or just another retread of Dr. Jekyll & Mr. Hyde? The movie was adapted from a novel by Paddy Chayefsky, who based it on pioneering work on sensory deprivation by John Lilly. Curiously, Chayefsky demanded that his name be removed from the credits. Believe it or not, this was one of Ken Russell's more restrained directorial efforts.