A man is tricked into trading places with a look-alike nobleman with murderous plans.

Englishman John Barratt, a French-language teacher at a small college, takes his annual holiday in France, where he reflects on his lonely, futile existence. Late in the evening of his first vacation day, John grows disconcerted when a man begins following him and ducks into a small pub. Moments later, he receives a shock when the man from the street appears and his features match John's identically. John agrees to have drinks with the man, who introduces himself as Jacques De Gué, a titled land-owner of the chateau St. Gilles, where he runs a failing family glass-making business. Unaccustomed to drinking, John soon reveals that he is single, with no family and frustrated with the purposelessness of his life. Learning that John has not arranged accommodations, Jacques suggests that he might find a room at his hotel. Upon reaching the hotel, Jacques tells John there are no extra rooms and invites him to share his accommodation. Although somewhat drunk, John agrees, then accepts champagne from Jacques who has, unknown to John, slipped a sleeping draught into the drink. The next morning, John awakens to find himself, dressed in unfamiliar pajamas and discovers that Jacques is gone. When Gaston, the De Gué family chauffeur arrives, John demands to know Jacques's whereabouts and upon discovering that his passport is missing, insists that Gaston summon the police to have Jacques found. Instead, Gaston telephones St. Gilles and on advice of Dr. Aloin, the family physician, Gaston tells John that Jacques has asked to meet him at St. Gilles. John agrees, but when he arrives at the chateau, is angered when Dr. Aloin does not believe his explanations about Jacques's disappearance and suggests that John is suffering from emotional duress. John is then flustered by the warm greeting from Jacques's young daughter, Marie-Noel, who believes him to be her father. When Marie-Noel reveals that her bedridden grandmother is anxious to see him, John follows her to Jacques's mother's room. There, he is surprised by the Countess De Gué's affectionate welcome, which gradually turns into an emotional outburst when the Countess demands a mysterious present from Paris. With the help of a maid, John goes through Jacques's suitcase and discovers several gifts, one of which holds several vials of morphine, which the maid promptly takes to the Countess. Uneasy, John finds his way to the drawing room where he is met by Jacques's wife, Françoise and his sister, Blanche, who have been advised by Dr. Aloin of John's story. John greets them pleasantly, but becomes alarmed when Blanche stalks out of the room and Françoise accuses him of cruelty. Confused, John flees outside, wondering how to deal with his predicament and is calmed by a chat with the precocious Marie-Noel. John spends the night in indecision, but, intrigued by the De Gué family, finally resolves to say nothing further of his true identity. At breakfast, John meets Jacques's brother-in-law, Aristide, who asks John about business discussions in Paris. Françoise, Blanche and Marie-Noel are confused by John's amiable, pleasant manner and interest in them. When John asks if he might inspect the foundry, the family members are bewildered. Marie-Noel then reminds John that he must drive her to her weekly music lesson in the nearby town of Villars and John plays a game with her in order to learn the directions there. Strolling in town, John wonders about Jacques's purpose for switching places with him, when he is nearly trampled by a horse ridden by an attractive woman, Bela. After speaking with Bela, John soon realizes that the affable woman is intimately acquainted with Jacques. John accepts Bela's invitation to tea at her small home and enjoys her company. Back at St. Gilles, John goes through Jacques's business papers and learns that Jacques has not visited the foundry in fourteen years. Later at the foundry, when pressed by the workers, John acknowledges that Jacques has not renewed their major contract. John then meets with the Countess to announce that he intends to renew the business contract even at unfavorable terms, rather than allowing the business to fail and put long-time employees out of work. Startled, his mother criticizes his decision and mentions a clause in a family contract that piques John's curiosity. John finds the contract, drawn up upon Jacques's marriage to the wealthy Françoise, which declares that should there be no male heir upon Françoise's death, her substantial wealth would pass to her daughter or her daughter's guardian, should she be underage. Françoise visits John and, disturbed to find him reading the contract, breaks down, declaring that Jacques has never loved her. Alarmed by Françoise's distress, John calms her by insisting the contract can be changed. John continues his masquerade at St. Gilles over the next several days and visits Bela again on his next trip to Villars. When John attempts to tell her the truth about himself, Bela admits she knew at once that he was not Jacques because his manner was so different. Relieved to find Bela sympathetic, John tells her about himself and the strange meeting with Jacques. Back at St. Gilles, John panics when he learns of a hunt set for the following day and of Jacques' reputation as a crack shot. To avoid participating, John deliberately burns his shooting hand at the foundry. One day some three weeks after the masquerade began, Gaston takes John aside to relay a summons from Bela. When John arrives at Bela's, however, she claims that she did not send for him but the two enjoy the afternoon together. Later, when Gaston drives John back to St. Gilles, they find a police investigator and Dr. Aloin there. The doctor informs John that Françoise has died after falling from her second-story window. At the inquest held at the chateau the next day, the Countess testifies that she was the last person to see Françoise alive. Blanche intercedes to declare that she overheard Jacques in Françoise's room and accuses him of murder. Gaston contradicts Blanche with his testimony of driving John to and from Villars. Realizing that Jacques intended John to be the scapegoat so that he could murder his wife for her money, John is not surprised when later he receives a call from Jacques to meet him that evening at the foundry. There, John berates Jacques for murdering his wife, then informs him that he refuses to give up his masquerade, believing he can help the family. Jacques scorns John's sentiment and at gunpoint demands that he depart. Unknown to Jacques, John has a gun and kills Jacques. The following morning, John goes to Bela to reveal that fate has decreed they remain together.