The French gentleman thief Arsene Lupin steals a priceless emerald from heiress Stacie Kanares while en route to Paris on the Orient Express , only to return it to the beautiful young lady upon meeting her. Learning that Stacie is bound for London, Arsene changes his travel plans and goes to England, much to the chagrin of Dubose, his valet. Upon his arrival in London, Arsene steals both Rembrandt's Laughing Girl and the Whitby Psalter , putting both Scotland Yard and French police detective Ganimard on his tail. Ganimard traces the elusive Arsene through his purchase of a rare case of wine, determining that he is at a cottage near Wainbridge Manor, Stacie's country estate. Stacie lives with her cousins, Charles and Bessie Seagrave, and Arsene quickly deduces that the debt-ridden Seagraves are trying to kill Stacie for her inheritance. In order to make Stacie a less attractive target for her cousins, Arsene decides to steal the emerald once again. After handcuffing Ganimard to his car, Arsene breaks into Wainbridge and steals the emerald, only to be discovered by Stacie as he attempts to leave. He then professes his love for her, but she doubts his sincerity after finding the emerald in his pocket. Arsene is arrested by Ganimard as he attempts to leave, but is cleared of all charges when Stacie returns the emerald to the safe. After arranging Ganimard's false arrest, Arsene rushes back to Wainbridge just in time to save Stacie from certain death. The Seagraves are arrested, and Arsene and Stacie agree to meet in Athens. As a sign of trust, Stacie places the emerald in Arsene's pocket, which inadvertently leads to the thief's arrest.