When Alice Turner is found dead in her room, her landlady is stunned to learn that the man with whom Alice has been living is not her husband. Although Alice's death is ruled a suicide, Thomas Turner, her real husband, is convinced that she was murdered. Meanwhile, Ronnie Marsh, as the other man now calls himself, moves to another town and rents a room from Hilda Fenchurch, a stenographer, and her mother. The women eagerly await the return of Anne, Hilda's younger sister, who has been away. The charming Ronnie tells the Fenchurches that he is a struggling writer, and he and Hilda rapidly become friends. During a weekend away, for which Hilda is footing the bill, Ronnie presents her with the wedding ring he removed from Alice's dead finger. He tells her that the ring belonged to his mother and offers it to her as an engagement ring. Hilda's happiness is threatened after Anne returns home, however. Learning that Anne has inherited $25,000, Ronnie switches his interest to the younger woman and assuages her guilt by insisting that he has never been in love with Hilda. Meanwhile, Hilda has begun to think that Ronnie is not what he seems. She finds a gun in his room and then learns that he has taken Anne dancing. Ronnie dismisses her concerns and tricks her into writing a suicide note by pretending he needs help with a story. Hilda's suspicions are aroused again when Anne's old boyfriend, Bunkie Taylor, tells her that Anne and Ronnie have been dating regularly and that Ronnie has been paying for the dates with money he earned from selling his stories. Furious, Hilda asks Ronnie to leave the house, but Ronnie responds that if he leaves, Anne will leave with him. For help, Hilda turns to one of her clients, psychiatrist Dr. Jane Silla, who meets with Ronnie and agrees that he is dangerous. Ronnie's plan to kill Hilda is interrupted when Dr. Andrew Lang, another of Hilda's clients, unexpectedly asks for Hilda's help in his laboratory one evening. There Hilda finds a test tube filled with the deadly botulism bacillus and steals it. Pretending to be Silla, Hilda invites Ronnie to the psychiatrist's beach house for dinner. When Lang tells Silla that he has discovered the missing test tube, the two rush to the beach house, hoping to prevent Hilda from committing murder. After dinner, Hilda tells Ronnie that she has poisoned him, and he becomes wildly agitated, but the two doctors arrive in time to reveal that the test tube was never opened. Exposed as a coward, Ronnie starts to leave, but Turner, who has tracked Ronnie, chases him until he dies in a fall. Later, Anne is reconciled with Bunkie, who has joined the Navy, and Lang finally gets up the nerve to invite Hilda to a concert.