Based on a play by Emlyn Williams, a man charms and is hired by an ailing lady, but her niece suspects he is a murderer.
Mrs. Bramson (May Whitty) learns that her maid Dora (Merle Tottenham) is upset about a man. A policeman says that a woman is missing. Mrs. Bramson questions Danny (Robert Montgomery) about Dora. Danny tells Olivia Grayne (Rosalind Russell) he is going to marry Dora. Danny asks Mrs. Bramson about her ailments and says she is like his mother. Mrs. Bramson likes Danny and hires him. Danny buys a shawl. Lawyer Justin Laurie (Alan Marshall) warns Mrs. Bramson she has too much money in her house, and she changes her will. Danny moves in. Justin asks Olivia why she won't marry him. Danny tells Olivia that she is good-looking without her glasses. Danny tells Mrs. Bramson that the shawl was his mother's, but Olivia removes the price tag. Danny helps Mrs. Bramson lie down and finds a sonnet Olivia dropped. Danny takes Mrs. Bramson for a walk in her wheelchair. Olivia asks Dora if she trusts Danny. Olivia, Dora, and the cook (Kathleen Harrison) search Danny's things and find a photo of him with the missing woman. Danny comes in and says he hates a spy. Olivia tells Danny he is acting and has no feelings. The woman's body without a head is found nearby.
Olivia goes to Justin, who says she can stay with his mother and him; but Olivia changes her mind and goes back. Inspector Belsize (Matthew Boulton) questions Danny, Mrs. Bramson, and Olivia. At night Danny finds Olivia up and asks why she hasn't married Justin. Tourists take photos of Mrs. Bramson. Olivia suspects that Danny drinks, and Danny learns that Mrs. Bramson wears the key to her safe around her neck. Olivia asks Danny if he was a butcher and tells him she could kill Mrs. Bramson. Olivia says he can't sleep. Inspector Belsize asks Danny why he didn't sleep in his bed the night of the murder. The inspector searches Danny's room. Danny denies a locked box is his, and Olivia tells the inspector it is hers. After the inspector leaves, Danny faints. Olivia revives him, and Danny takes the hat box. Olivia calls Justin that she is coming and then warns Mrs. Bramson that she is terrified.
Mrs. Bramson asks Danny if Olivia is a thief. Dora and the cook leave. Mrs. Bramson calls Danny but finds no one, panicking. Danny comes in and gives her wine to make her sleep. He gets rid of her with a pillow, robs the safe, and gets kerosene. Olivia comes in and says he killed her. Danny says Olivia wanted to be alone with him. Danny tells Olivia he won't be found out, and the house will be gone; but Inspector Belsize, Justin, and the police come in and handcuff Danny. Olivia thanks Justin, and the police take Danny away.
Fine acting enhances this mystery drama that contrasts the pleasing personality of Danny with his gruesome deeds. Mrs. Bramson is completely taken in by his manner, but Olivia suspects correctly it is an act. Similarly audiences are entertained by such mysteries that are not real. Yet how many are also fascinated by gruesome murders that are real?