In this frothy romantic adventure, Marlene Dietrich plays Madeleine de Beaupre, a devious jewel thief. After sneaking a valuable string of pearls away from jeweler Aristide Duval (Ernest Cossart), Madeleine attempts to flee Paris, leaving a trail that will instead implicate psychiatrist Dr. Pauquet (Alan Mowbray). While headed for the Spanish border, she nearly runs into Tom Bradley (Gary Cooper), an American auto engineer vacationing in Europe. Madeleine spots Tom again as she waits to go through Spanish Customs; worried that the stolen pearls will be found in her handbag, she slips them into Tom's pocket. After they both make their way through inspection unscathed, Madeleine flirts with Tom in an attempt to get the valuables back; he's too shy to respond in kind, so she gets his attention by trying to "repair" the engine of her car with a hammer. Madeleine lures Tom to the San Sebastian estate of her partner in crime, Carlos Margoli (John Halliday). It doesn't take long for Tom to figure out what Madeleine and Carlos are up to; however, he also knows that he's fallen in love with her, and he is willing to play along if it allows him to be near her. Carlos was originally to have been played by John Gilbert; Halliday was a last-minute replacement after the one-time silent screen star died a week before shooting was to begin.