A 40-year-old woman swaps her sophisticated lover for a young law student.

For 5 years Paula Tessier, a 40-year-old Parisian interior decorator, has been the mistress of Roger Demarest, a philandering business executive. Though well aware of his numerous affairs with other women (all of whom he calls Maisie), Paula remains faithful, hoping that eventually Roger will marry her. Then one day she meets Philip Van der Besh, the 25-year-old son of one of her wealthy American clients. When the young man becomes hopelessly enamored of her, Paula is at first embarrassed, but gradually she begins to respond to his love. Consequently, when Roger leaves on a business trip and refuses to take her along, Paula gives in to Philip's pleas and allows him to move into her apartment. Roger returns and reacts to the affair with anger, rather than show how deeply he has been hurt. He goes off with one woman after another, but he is unable to forget Paula and finally asks her to marry him. Delighted, Paula tries to break the news to Philip as gently as possible, but he runs tearfully from the apartment. Though Paula has at last become a wife, Roger continues his bachelor social life.