Millionaire sportsman Hiram Brighton hires gumshoe Michael Shayne to keep his spoiled daughter Phyllis away from racetrack betting windows and roulette wheels. After Phyllis slips away and continues her compulsive gambling, Shayne fakes the murder of her gambler boyfriend, who is also romancing the daughter of casino owner Benny Gordon, in order to frighten her. When the tout really ends up murdered, Shayne and Phyllis' Aunt Olivia, an avid reader of murder mysteries, both try to find the identity of the killer.