Dr. Constance Petersen (Ingrid Bergman) is a psychiatrist at Green Manors mental asylum. The head of Green Manors has just been replaced, with his replacement being the renowned Dr. Anthony Edwardes (Gregory Peck). Romance blossoms between Dr. Petersen and Dr. Edwards, but Dr. Edwards starts to show odd aversions and personality traits. It is discovered that he is an impostor, and amnesiac, and may have killed the real Dr. Edwardes. Dr. Petersen is determined to discover the truth through unlocking the secrets held in the impostor's mind, a process which potentially puts her and others' lives at risk.