In Paris, 25-year-old Lucile is the beautiful, carefree mistress of Charles, a wealthy, kind-hearted, middle-aged businessman. She refuses to work and enjoys a life of luxury and comfort thanks to Charles, but does not feel true love for him. When she meets Antoine, a charming but penniless young
publisher's reader who is the lover of an older socialite named Diane, the two instantly fall in love and begin an affair, regularly spending the afternoons together at his
one-room apartment. While Charles is on a business trip to New York City, Antoine suggests that Lucile move in with him, telling her that she must choose between him and Charles. On the day of Charles's return, Lucile goes to wait for him at
Orly Airport, while preparing to tell him that she is leaving him. Upon learning that his flight will be delayed, she worries that his plane may have crashed, but is relieved when he finally arrives. Unnerved by the thought of Charles dying, Lucile calls to tell Antoine that she has not yet broken up with Charles, upsetting Antoine. At the birthday party of Johnny, a mutual friend, Antoine makes a scene when Lucile refuses to dance with him, prompting him to leave. Antoine later ends his affair with Diane, while Lucile accompanies Charles to
Saint-Tropez. Upon learning from Johnny that Lucile is alone in Saint-Tropez and has been drinking excessively, Antoine promptly goes to meet her and they spend some time together at the seaside. Back in Paris, when Lucile breaks up with Charles, he grows agitated, declaring that he will always love her and predicting that Antoine will come to resent who she is, but she leaves with Antoine anyway. Lucile and Antoine are initially happy together, and he finds her a menial job in a publishing firm, but she quickly grows bored and quits the job after a month without informing Antoine. He eventually discovers her ruse and becomes angry but decides to let her have her way. When Lucile becomes pregnant by Antoine, they plan to move into a larger apartment in a
housing project. However, she later tells him that she has no desire to keep the baby and that Charles has agreed to fund her abortion at a Swiss clinic. Antoine is upset at first but ultimately agrees to accompany her to
Geneva for the procedure. Some time later, Lucile accepts Charles's invitation to accompany him to a
Mozart concert, and they spend the night together. The next morning, she goes to Antoine's apartment and finds him asleep. Tempted by the lure of her former life, Lucile calls Antoine from the café downstairs and ends their relationship before returning to Charles. ==Cast==