Well-to-do bourgeois, highly respectable in appearance, Jacques Etienne, his wife, Jacqueline and their two eighteen-year-old children, Stéphane and Bénédicte, lead a peaceful and rather boring life in the vast family home. But everything explodes when Bénédicte brings home Sweety, a young girl completely foreign to their sanitized world, whose innocent face hides Machiavellian designs that she will immediately strive to accomplish in the square. In turn, she will seduce all the members of the family and make them discover, not without ulterior motives, physical pleasure, allowing them to satisfy their most secret desires.