From the time of their meeting in 1912, Jules and Jim share a close friendship. Shortly before the First World War, Jules marries Catherine (Jeanne Moreau), a willful young woman the two men have befriended, but, after the war has ended, his relationship with her deteriorates rapidly. When Jim comes to stay with the couple and their daughter, he begins a relationship of his own with Catherine, having been urged to do so by Jules, who hopes that if his wife is involved with his friend she will not leave him.