Driven to distraction by the howling of the dog next door, Arthur Cartwright insists that lawyer Perry Mason attempt to stop it. He also wants to make a will and leave his money to the wife of Clinton Foley, the dog's owner. He explains that Evelyn, the woman now living with Foley as his wife, is not actually married to him. After he receives a copy of Cartwright's will in the mail, Perry investigates the dog problem. He sees that Foley is building an addition to his garage. While Perry talks to him, Foley receives a note announcing that Evelyn has run away with Cartwright. Perry's men investigate and learn that Evelyn was married to Cartwright and Foley took her away from him, leaving his own wife, Bessie Foley, behind. While he is watching the Foley house, one of Perry's men sees Lucy Benton, Foley's housekeeper, drive away. Later a cab arrives with Bessie Foley. She asks the driver to go next door and tell Cartwright that she is there. In the house, she and Foley quarrel and two shots are fired, killing Foley and the dog. Perry arrives after Bessie leaves and discovers the body. He tracks Bessie to her hotel. Bessie admits that Foley was consistently unfaithful, but she denies killing him. Perry advises her to say nothing to the police and does not allow her to testify at the trial that follows. During the trial, Perry demonstrates that both Cartwright and Evelyn are dead and buried under the foundation of Foley's garage. He proves that, with her left hand, Lucy wrote the letters that seemed to come from Evelyn. He claims further that the dog never would have attacked Bessie, necessitating her killing him, because the dog loved her. Perry proves that Foley killed Cartwright and Evelyn, and Bessie is acquitted. In his office, however, Perry brings in a dog that looks just like the murdered dog. When the dog delightedly greets Bessie, Perry admits that the dog that died was not Foley's dog. That dog had been put in a kennel because of his howling, which had drawn Cartwright's attention to Evelyn's murder and led to his own murder. Sure that Bessie killed Foley in self-defense, Perry cleverly did not allow her to testify and now sends her away with the dog.