The Third Lover (1962)

André Mercier, a journalist known as Albin Mercier, is a failed, embittered writer. Sent to cover an event in Germany, he gets to know Andreas Hartmann, another writer who, for his part, has not... failed. The successful Andreas is married to Hélène, a beautiful Frenchwoman. Both attracted to her and jealous of the couple's happiness, Mercier decides to shatter it. Taking advantage of the absence of Andreas, off on a business trip, he tries to seduce Hélène and to become her lover. But things do not go according to plan...