A doctor is murdered, and suspicion falls on his girlfriend. The police discover she has an identical twin, and each sister provides the other with an alibi. A psychiatrist is called in to determine which of the women is the killer, but he begins to fall for one of his suspects. Mystery, starring Olivia de Havilland in a dual role, alongside Lew Ayres and Thomas Mitchell.

A sister and her disturbed twin are implicated in a murder and a police detective must figure out which one's the killer.