Detective Philo Vance solves a double murder that starts as an obvious suicide case in this adaptation of S. S. Van Dine's novel.
At a dog show Hilda Lake (Mary Astor) gets angry at her uncle Archer Coe (Robert Barrat) for refusing to loan her money. Brisbane Coe (Frank Conroy) refuses to see his brother Archer. Hilda's show dog is stolen and found killed. Doris Delafield (Helen Vinson) tells Archer to get out of her apartment, and Archer tells Grassi (Jack La Rue) his big art deal is off. Archer's Chinese cook Liang (James Lee) complains to Archer about his selling Chinese art treasures. Archer is found dead with a gun in a locked room by his butler, and it is reported as a suicide. Knowing Archer would not kill himself while hoping to win the dog show, Philo Vance (William Powell) cancels his voyage and investigates. Hilda has her own motive for murdering her uncle and suggests other suspects too. Raymond Wrede (Ralph Morgan) wants to marry her, but she tells him she is going to marry Tom MacDonald (Paul Cavanagh). Philo stops Hilda and Tom from going to England.
Dr. Doremus (Etienne Girardot) examines the body and finds a skull fracture but that death was caused by a stab in the back before the gunshot. Brisbane Coe is found dead in a closet, stabbed by the same weapon. Philo shows how Brisbane used string and a needle to lock the door from the outside. Philo's dog finds a wounded dog belonging to Doris next door. Sergeant Heath (Eugene Pallette) questions Doris and cancels her boat reservations with Grassi. Philo finds a vase fragment with blood on it under the rug. Philo questions Raymond and the cook Liang, who tells what he saw and how he took the poker and the vase fragments. Grassi's fingerprint is found on the fragment. Doris tells district attorney Markham (Robert McWade) she killed Archer in his bedroom, but Philo believes she is protecting Grassi. Tom is found stabbed, but he survives. He and Hilda plan to leave. Philo explains what the killer did, what Archer did before he died, and how Brisbane shot the dead Archer before locking the room and being killed by the murderer, who returned from next door to finish off Archer. Philo says any of seven people could have done it and has Markham release all the suspects. Philo incites an argument between Raymond and Tom in which Raymond assaults Tom and reaches for the poker. Philo looses the dog, and Raymond confesses.
This murder mystery is cleverly contrived with numerous suspects having motives. The audience is kept guessing until the end as the persistent Philo adds clue to clue until the whole puzzle comes together.