John Barratt (Alec Guinness), a lonely, discontented teacher of French at a British university, vacations in France. There, by chance, he meets his double, French nobleman Jacques De Gué (Guinness again). They become acquainted. Barratt becomes drunk and accepts De Gué's invitation to share his hotel room. When he wakes up the next morning, Barratt finds himself alone in the room, with his clothes and passport missing. De Gué's chauffeur Gaston (Geoffrey Keen) shows up to take his master home, and Barratt is unable to convince him that he is not the nobleman. Gaston calls Dr. Aloin (Noel Howlett), who diagnoses the Englishman as suffering from schizophrenia. A bewildered Barratt allows himself to be taken to De Gué's chateau, where he meets "his" family: daughter Marie-Noel, wife Françoise (Irene Worth), sister Blanche (Pamela Brown) and formidable mother, the Countess (Bette Davis). None of them believe his story - it appears that De Gué is a malicious liar - so Barratt resigns himself to playing along. As time goes on, he feels needed, something missing in his sterile prior life. The next day, brother-in-law Aristide (Peter Bull) discusses business with him. Later, in the nearby town, Barratt is nearly run down by De Gué's mistress, Béla (Nicole Maurey), on her horse. He spends the usual Wednesday afternoon tryst getting acquainted with her. The next time they meet, before he can confess the truth, she informs him that she has already guessed it. Barratt delves into the neglected family glass-making business. He decides to renew a contract with the local foundry, even on unfavourable terms, to avoid throwing the longtime employees out of work. The Countess is upset by his decision and mentions a marriage contract. When Barratt investigates, he learns that Françoise's considerable wealth, tied up by her businessman father, would come under his control if she were to die. Françoise finds him reading the contract and becomes very upset, accusing him of wanting to