Two precocious youngsters, Sara, 12, and Ben, 11, check in with their industrious father and their governess, Miss Oliver. Ben and Sara play a prank on Billy by faking an intruder attack. After Ben and Sara overhear an argument punctuated by a pistol shot, they see someone in a Burberry coat sprinting away. They find a dead woman's body in the front seat of a car, but when they take their father to the scene, the body is gone. When they inform Billy, he walks away. Christine's aunt Addie, a wealthy widow, is in town for a reunion with her lover Luke. After Peter exposes Luke as a hustler, Christine informs Addie about Luke's questionable character. Already aware of Luke's hustling, Addie chastises her niece for meddling. Ben sees Miss Oliver in a Burberry coat and is convinced that she is the murderer. Ben and Sara uncover evidence that she has killed the real Miss Oliver and has assumed her identity. As the impostor attempts to kidnap Sara at gunpoint, the police and Billy arrest her.