Ann Sutton, Gene Tierney, the wife of Richard Conte Dr. William Sutton, a successful psychoanalyst, is caught shoplifting in an upscale Los Angeles department store and loses consciousness when apprehended. She is saved from scandal by the smooth-talking hypnotist David Korvo, Jos Ferrer, who persuades the store officials to put the mermaid pin she stole on her credit account and not prosecute. Korvo pressures Ann into coming to lunch with him, and she is relieved when, instead of accepting the blackmail payment she thinks he is after, he tears up her check and the store record of her shoplifting, and promises to help her.
Overcome with shame surrounding her secret, Ann begins experiencing insomnia. She attends a sophisticated party with Korvo, where she meets Theresa Randolph, Barbara O'Neil, a former lover of Korvo's and one of her husband’s patients. Korvo hypnotizes Ann at the party and instructs her to sleep, which works, but she does not respond to other orders. Ann meets Korvo at the hotel where he lives for further therapy sessions, but refuses to go up to his suite and insists on talking in public in the hotel bar. Korvo distracts her and takes the martini glass with her fingerprints on it, as well as her scarf.
Later that night, Ann enters a trance, takes two vinyl records from her husband’s patient archives and brings them to Theresa’s house, where she hides them in a closet before discovering Theresa's murdered body in the den. Ann's entry into the home sets off a silent alarm, and police arrive moments later. Before regaining full lucidity, Ann confesses to hating Theresa. Her scarf is found in the home, and the martini glass is found in Korvo's apartment. Police charge her with murder, presuming she strangled Theresa out of jealousy over Korvo.
Ann's husband, Dr. William Sutton, and his lawyer, Martin Avery, believe she is innocent and that Korvo framed her. William recalls that Theresa had informed him during their therapy sessions that Korvo had extorted her for $60,000. It is found, however, that Korvo has a cast-iron alibi: at the time of the murder and ever since, he has been in the hospital weak and prostrate after a gall bladder operation. The police lieutenant in charge of the case, Colton, is sure this rules him out as a suspect.
When William leaves the police station, Avery and Colton persuade Ann to confess her real guilt. Instead, she only confesses to her kleptomania, stemming from her indigent childhood; when William wanted her to ignore her own riches and live on his small salary at the beginning of their marriage, he triggered Ann's childhood trauma, and she returned to her habit of shoplifting. William's theory accounts for Korvo's apparent spike in body temperature observed by the medical personnel on the day of Theresa's murder. William presents his theory to Colton and suggests they bring Ann to Theresa's home to find the records, but Colton dismisses him.
In the hospital, a nurse casually comments to Korvo about the search for Theresa's patient records. Korvo hypnotizes himself again, sneaks out of the hospital, and drives to Theresa's house, where he retrieves the records and starts playing them: They reveal Theresa's voice implicating Korvo in her extortion. Simultaneously, after some contemplation, Colton comes to believe William's theory may be true, and he accompanies him and Ann to Theresa's house. Once there, Korvo menaces Ann with a gun, attempting to force William and Colton out of the room. As his trance begins to wear off, Korvo realizes he is bleeding to death from his surgical wound. In a moment of bravado, he tries to flee the house, but collapses and dies. Colton releases Ann into the care of her husband, and they happily embrace.
