Marion (Emmanuelle Bercot), a 30-year-old woman, attends the 13th birthday party of her godson, Léo (Kevin Goffette). There, she meets Léo's best friend, Clément (Olivier Guerritée), a bold and confident 13-year-old boy. What begins as playful teasing rapidly evolves into an intense, taboo fascination as Marion becomes obsessed with the young adolescent. Despite the severe social boundaries, moral taboos, and condemnation from those around her, Marion pursues a secret emotional and physical relationship with Clément, forcing both to navigate an unequal and destructive dynamic.