Sarah Morton, a middle-aged English mystery author, who has written a successful series of detective novels, is having writer’s block that is impeding her next book. Sarah’s publisher, John Bosload, offers her his country house near Lacoste, France for some rest and relaxation. Sarah takes him up on the offer, hinting that she hopes John may come and visit as well. After becoming comfortable with the run of the spacious, sun-filled house, and meeting the groundskeeper Marcel, Sarah’s quietude is disrupted by a young woman claiming to be the publisher’s daughter, Julie. She shows up late one night explaining that she’s taking time off from work herself. She eventually tells Sarah that her mother used to be Bosload’s mistress, but that he would not leave his family.
Julie’s sex life consists of one-night stands with various oafish men, and a competition of personalities develops between the two women. At first, Sarah regards Julie as a distraction from her writing. She uses earplugs to allow her to sleep during Julie’s noisy nighttime adventures, although she nonetheless has a voyeuristic fascination with them. Later she abandons the earplugs during one of Julie’s trysts, beginning to envy Julie’s lifestyle. Sarah sneaks into Julie’s room and steals her diary, using it in the new novel she’s working on. The competition comes to the fore when a local waiter, Franck, is involved. Julie wants him but he appears to prefer the more mature Sarah, having struck up a relationship with her during her frequent lunches at the bistro.