Lady Diana Winham is beautiful, wealthy and a widow, so she's courted. She travels Europe in luxury trains, earning her nickname. One of her riches, a uranium deposit in a South American country, attracts the attention of international secret agents. Lady Diana is at the center of a spider's web, with the French, British and Germans all trying to get their hands on her. Helped by the love of Armando, whom she met in San Miguel, she gives the deposit to her secretary Gérard as a reward for his services.