While Sûreté inspector Gabriel Hanaud visits the London home of his friend Mr. Ricardo, they receive a visit from Carradine, a young socialite with a disturbing story. A beautiful young woman he met at a costume party has appealed to him for help. Obsessed with a rich American woman's pearls, this young woman went to steal them from the American's hotel room ... only to find a gang of thieves, who overpowered her. She woke up hours later, alone in the room except for a dead body. Can Hanaud prove her innocence, and bring the real murderers to justice?