Reformed jewel-thief Sophie Lang, tired of being questioned by the New York City police every time a jewel disappears, decides to head for California, and is hiding in the train-compartment of film-writer Eddie Rollyn. Rollyn is working on a story for film-star Helga Roma, who is also aboard the train with her manager, Steve Clayson. Thinking there is a story in Sophie's flight, Rollyn agrees to help her out and hide her from the police if she will help him with his film story. NYC Detective Archie Banks is aboard the train guarding the Sultan of Padaya, owner of a precious gem called "Star of the World." Archie gets the Sultan's consent to allow Miss Roma to wear the gem in a film, feeling that the publicity will entice Sophie out of retirement to steal the stone, and he can get some publicity himself by capturing her in the attempt. But Crayson steals the jewel and tries to escape with it, but is captured by Rollyn. Clayson escapes and finds Sophie. He tells her that Rollyn is an ex-thief, and she must help him steal the diamond again, or he will expose Rollyn and ruin his career.