Mathilde (Paradis), a melancholy 17-year-old without parents, drives the story. François (Cremer), her philosophy teacher, finds her and wants to help her learn. He begins visiting her daily to help her with her homework and study skills. Mathilde hints that she likes 47-year-old François. Despite his resistance, he falls for her. They fall in love, but his wife (Mikaël) and the school must remain unaware.