Catherine is a rebellious pre-teen who lives with Maryse, her divorced mother. Their new neighbour, David, a dentist, lost his wife and his eldest daughter in a car accident several years ago. Since then, he is overprotective of his other daughter, the withdrawn Ariane, who is in the same class as Catherine. The two neighbours become friends and Catherine tries to free Ariane from her father’s grip, while teaching her to smoke and introducing her to boys. One day, David stops his daughter from taking part in a school outing by putting a drug into her glass of juice. But when Liette, Ariane’s babysitter, discovers the truth and threatens to expose him, David kills her. Catherine begins to suspect what has happened, and is upset when she realizes her mother is becoming attracted to him.