The plot centres around moody 17 year old Mathilde (Paradis) who lived separated from her parents. Her philosophy teacher François (Cremer), happens to stumble across her path and is eager to help her learn more. He starts to come over to her house everyday going over her homework, and teaching her the art of the study. Eventually, Mathilde starts placing little hints that she finds the 47 year old François attractive. He tries to resist her, but he finds himself falling for her as well. They soon blossom into a passionate love, but they must keep their affair a secret from his wife (Mikaël) and the school. Later François's wife finds out about the affair because her husband comes home late and Mathilde calls his house until he answers. Mathilde becomes obsessed and jealous of his wife, starting to send her messages and breaking the glass windows in her store - his wife tries desperately to find a solution to it. Soon after, she sets an ultimatum to François, by letting him choose between her and Mathilde. He understands the consequences of his decisions and stops the affair. Mathilde starts a relationship with her classmate and tries to make François jealous. One day, after Mathilde's friends have looted François's wife's shop, angry François drags Mathilde out of his class, seeking an explanation from her. Soon he cools down and the two share a passionate kiss. But a camp of schoolboys happen to see this trough a class window. After that, François is fired and Mathilde is expelled from school. His wife decides to divorce him and he moves to another city and starts teaching there. One year later, he gets a phone call from police, who says Mathilde is dead, he comes to see the body and is shocked by the death of his true love. It turns out that Mathilde had bought an apartment two months ago, next to his school and that she had a perfect view from her apartment window to his classroom. She had lived as a recluse. She used to sit all day looking out of the window. She died of yearning. At the end, François goes to sit on the sand of the beach and watches the ocean, reminding Mathilde's last words, written on her apartment wall: "There's the ocean, François". The meaning of this phrase refers back to her mother's suicide description, in which she says that she felt like she "was merging with the ocean." Those were the mother's last words.