In a snowball fight between schoolboys the handsome Dargelos hits the chest of Paul, who drops unconscious to the ground. Paul has a deep affection for Dargelos, and later denies that there was a stone in the snowball that hit him. Back home Paul's sister Elisabeth takes care of him. The teenage siblings live together in one room, where they have developed several private games. Paul's schoolmate Gérard is secretly enamored of Elisabeth, and often stays with them. When Elisabeth introduces her new friend Agathe to Paul, he recognizes that she resembles Dargelos strongly, and immediately falls in love with her. Elisabeth marries a rich young American Jew, Michael, but he dies in a car accident the day after the wedding. Elisabeth inherits his big apartment with 18 rooms and a gallery, and the four friends move into it. Paul sleeps in the gallery, where he builds a replica of the siblings' old room. Both Paul and Agathe are secretly enamored of the other. When each of them reveals this to Elisabeth, she gets jealous, and starts developing a sinister plot to turn them away from each other.