A woman slowly discovers that her artist husband is a deranged killer.

While on vacation in Scotland, Sally Morton meets and falls in love with painter Geoffrey Carroll, but ends the relationship when she learns that he has an invalid wife and a daughter. In London, Geoffrey, using a pseudonym, buys a supply of poison from pharmacist Horace Blagdon. He then sends his young daughter Beatrice away to school and takes over the nursing duties. Two years after the death of Geoffrey's wife, he and Sally have been married a year and live outside London with Bea. Geoffrey's portrait of his first wife as "Death" is superb, but Geoffrey currently faces difficulties in the studio and is irritated when Charles "Penny" Pennington, Sally's former fiancé visits with wealthy Mrs. Latham and her attractive daughter Cecily. Cecily greatly admires Geoffrey's recent one-man show and wants him to paint her portrait. At first Geoffrey gruffly turns her down, but later, because he needs the money to pay Blagdon's blackmail demands, agrees to do the work and begins an affair with Cecily. When Sally later becomes ill, the alcoholic Dr. Tuttle attributes her symptoms to a nervous disorder. One afternoon, Cecily invites Geoffrey to come to Rio de Janeiro with her, and he asks her to wait until Sally recovers from her illness. Geoffrey again plans to send Bea to a prestigious boarding school, but asks her not to tell Sally. Later, despite her weakness, Sally prepares a small dinner party for the Lathams and Penny. She asks to see Geoffrey's new painting, but he angrily refuses to let her near the studio. He is also miffed that Penny will be at dinner. Geoffrey then travels to London to meet Blagdon, who has demanded another payment, after lying to both Bea and Sally about the purpose of the trip. While he is gone, Sally, who has long suspected his affair with Cecily, finds a rose that she dropped on her afternoon visit. When Sally finds Bea packing for school, she questions the girl and learns that she was also suddenly sent to school before her mother died. To Sally's surprise, Bea tells her that her mother was not an invalid, but became sick with the same symptoms Sally now displays after Geoffrey returned from Scotland. When Bea then reveals that Blagdon is a chemist, Sally suddenly suspects that Geoffrey is trying to kill her. With Bea's help, she sneaks a look at the portrait Geoffrey is painting of her and is so shocked by the horrible image that she faints. Penny is concerned by Sally's fainting spell, believing it may have been caused by anxiety over a strangler who has been seen in the neighborhood, but she reveals nothing to her friend. Geoffrey returns after dinner, having killed Blagdon, and covertly tells Cecily that he will go with her to Rio. After the maid, Christine, leaves to drive Bea to school, Sally asks Geoffrey some pointed questions. Surprised by her changed manner, he offers to get her evening glass of milk. Sally secretly throws the milk out the window and retires to her bedroom, taking a gun that Penny loaned her. Later, Geoffrey sees the spilt milk on the window sill and realizes that Sally suspects him. He decides to make her murder seem like the work of the strangler and breaks into her bedroom. A terrified Sally manages to call Penny, but Geoffrey cuts the phone line before she can tell him what is happening. Geoffrey explains that Sally's death would help his work live again, just as the death of his first wife did. Sally holds Geoffrey at bay with the gun until Penny arrives with the police. Despite the presence of the men outside Sally's bedroom door, Geoffrey starts to choke her, but finally stops, just as the police break through the door.