Diane, a 14-year-old girl, lives with her younger brother Marc and her father Christian, and she is eager to explore her sexuality. When she visits her friend Antoine, the two strip naked and slip into bed together. As Antoine kisses her and calls her beautiful, she tells him that she would prefer not to talk. He apologizes, and they try to find comfortable positions, but awkwardness soon takes over and they decide not to have sex. Antoine then takes her back home. There, her father catches her watching hardcore pornography and, despite her refusal, he demands she turn it off before exasperation drives him away.
During school, Diane’s friends discuss whether losing one’s virginity is painful. Diane meets with Antoine again, and they briefly hang out at his house. He invites her to stay, but she leaves for her own place. Through her window, she notices her new neighbor, Julia, while the girl’s father berates her. Annoyed, Julia pulls the curtains shut. At dinnertime, Julia introduces herself and asks for help finding a local piano teacher, and Christian and Diane promise to assist.
At school, Diane approaches Julia with a potential piano teacher, but Julia explains she only said that to meet Diane. The two form a friendship, and Diane invites Julia to a party. Julia tells her parents she will sleep over at Diane’s house, but Christian has no concerns about the arrangement. Diane brushes off Antoine and goes off to find Julia, who is about to ride in a car with two boys. Julia invites Diane to join, on the condition that Diane not interfere with Julia’s choices. As Julia and a boy have sex in the car, Diane and the other boy exit. After the second boy becomes aggressive and sexually harasses Diane, the two girls walk home.
Diane is shocked to find her father with a woman in the house, and the noise of their intercourse keeps her awake. In the morning, she confronts him about his irresponsibility, noting that he has not woken Marc for school. Diane is hurt when she sees Antoine and Julia together at school. After football practice, she wanders into the male showers completely naked, and the Hockey coach calls her father to pick her up. As they drive home, Diane asks Christian whether he is sexually attracted to her, and she becomes annoyed as Christian fumbles for a thoughtful answer.
As Julia and Diane grow closer, they flirt and share a kiss. Their families become more friendly, and Diane goes on vacation with Julia and her parents. Julia seduces a bartender. Although Diane initially refuses to join them in a threesome, she later knocks on the door and watches the two have sex. Julia encourages Diane to have casual sex with a man at a club, but when he demands oral sex, Diane insists that she and Julia leave. Later, the two girls accompany Christian and Marc on a trip, and Julia again flirts with Christian despite Diane’s discomfort; the group engages in a threesome with a local man, Paul.
Julia flashes Christian, and as he stares at Julia, Diane chastises him. After Christian becomes drunk that night, Julia kisses and undresses him. Christian weakly pushes her away, telling her it’s a bad idea, but she continues to seduce him. He eventually gives in, and the two have sex outside against a tree. When Diane searches for her friend, she is horrified to see them and slaps her father. Christian apologizes, and as she storms off, he pursues. After he retrieves her, Diane asks Julia whether she would run away with her if asked; disinterested, Julia says she would not, and Diane walks into a busy road, prompting concern from the others. The film ends with Diane standing on the other side of the road, smiling.
