Two criminals are stalking the streets of London one dark night. Frank Clemmons (Dirk Bogarde), a cocky young man, holds psychiatrist Dr. Clive Esmond (Alexander Knox) up at gunpoint, but Dr. Esmond manages to overpower him. Frank has two options; he can go to prison or he can be a guest at Dr. Esmond’s house where he’ll be a human guinea pig subjected to Dr. Esmond’s scrutiny, which aims to cure him of his criminality. Frank agrees upon the latter.