Stephane Margelle ( Jean-Paul Belmondo ) is an industrial magnate living on the Riviera. He is married to a beautiful woman : Sophie. He is the ultimate Casanova. Whether aboard a ship, train or helicopter, no woman can resist his charms. Everything is fine until the day he drives his wife to the airport and meets an 18 years old girl, Julie ( Sophie Marceau ). He takes her through the usual paces : the restaurants, the nightclubs and finally, his place. But the plot thickens : his wife's flight has been cancelled and she returns home to find him with his new conquest. Stephane's only way out is to pretend that Julie is his daughter. But Julie, Stephane's wife and Julie's mother team up to teach the unknowing Stephane a lesson.