At a dinner party at her aunt Edith's, Penelope "Penny" Parker makes the acquaintance of debonair Simon Templar. While attracted to her, Simon is more interested in the actions of another guest, Bruno Lang. As the party breaks up, Lang finds a note in his car from "The Saint," a detective well-known on both sides of the Atlantic. Penny, suspecting that Simon is The Saint, follows him to Lang's home, where Simon steals a document out of Lang's safe. As Simon and Penny escape together, they discover a beaten man stumbling along the road. After getting the man medical attention, Simon learns that he is Count Stephen Duni, who was kidnapped and forced to print £1,000,000 worth of counterfeit bills. Duni names his kidnapper as Kussella, a business associate of Lang's. Simon leaves Duni under the name of Claud Teal in a hotel run by Mrs. Buckley. The real Teal, an inspector at Scotland Yard, suspects Simon of the robbery at Lang's house. Penny amateurishly trails Kussella to a tobacco shop, where she, in turn, is kidnapped. Kussella offers Simon to trade Penny for Duni. Simon agrees, but with the help of his valet, Dugan, manages to release Penny from Kussella's clutches before the trade. The group goes to Mrs. Buckley's hotel, where they learn that Duni has been killed by an unknown assassin. Teal arrests Simon for the murder, but only as an act to confuse the real killers. Simon goes to Duni's embassy, where he impersonates Teal and meets Stengler, Duni's killer. Simon and Penny then go back to the tobacco shop, only to discover that the crooks have left. Simon calls Dugan, who tells him that he has captured Stengler and Lang at Lang's home. No sooner does Dugan hang up the phone, however, then Kussella arrives and turns the tables on the valet. Simon and Penny arrive at Lang's home, and are immediately captured. Lang gives Simon one hour to return his stolen document, or he will kill Penny and Dugan. At his car, Simon pulls out a hidden knife, stabs Lang and hides his body in the trunk. Simon goes into the basement to rescue Penny and Dugan, then captures Kussella and Stengler. The chauffeur arrives and accidentally shoots and kills Kussella instead of Simon. Teal arrives next, and Stengler claims that Simon killed Kussella after kidnapping Lang and stealing one million pounds. At Scotland Yard, Stengler is brought into Teal's office, where he is confronted by Simon, Peggy, Dugan and Blake, a member of the Secret Service. Lang is then brought into the office, having been arrested for espionage and murder, and he tells Simon that he finally met a man smarter than himself. Simon takes Peggy back to her aunt, fearful of becoming a brow-beaten husband like Teal. As the two leave, Dugan says, "I thought she had him." Teal, so used to listening to his wife, replies "Yes, dear."