Ducobu goes on holiday in the south of France.

The day she turns 40, Marguerite Flora, a successful rep for a nuclear power company, begins receiving letters she'd sent to herself at age seven. The letters tell her what to do if her life hasn't turned out the way she thought it should, when she was living in poverty with her mother and brother in a small village in southern France. She decides to go back to her birthplace to get the lawyer to stop the letters, but also to visit her childhood sweetheart and her long-forgotten brother, in order to find peace within herself.

Ducoboo is a very inventive dunce and joker, he is very resourceful at finding new ways to copy from his neighbor, to cheat or to defy the teacher's authority.

Back to school for Ducobu, Léonie Gratin and Latouche. But this year, a major rival for Ducobu arrives at school: TGV, the king of cheating 3.0. While the financial situation of Saint-Potache becomes disastrous, the two dunces will have to unite their creativity to win a song contest and save their school.