The man is shown conducting a chorus and is informed his mother has died. He returns home for the funeral where an old friend arrives with their late teacher's diary. The diary describes how in 1949 their teacher, Clement Mathieu, was hired at a boarding school for difficult boys. He forms a choir to teach the boys music which improves their behavior and happiness. However, Mathieu is later fired for breaking rules, though he had saved the boys' lives from a fire. Upon his dismissal, the boys throw paper airplanes with messages out the window, touching Mathieu. He boards the bus to leave but one boy insists on coming with him.

2. Story 50 years after the main story takes place, a man is shown conducting a chorus. While conducting, he is informed that his mother has died. After the performance, he returns home for the funeral. Soon, an old friend called Pépinot arrives at his door with a diary. It is the diary of their teacher, Mathieu, and they read it together. In France in 1949, Clément Mathieu, who in his own words has failed at everything else, arrives at the gates of Fond de l'Etang (Bottom of the Swamp), a boarding school for "difficult" boys .On discovering the boys singing rude songs about him behind his back one night, Mathieu, who is a musician and composer, forms a plan - he will teach them to sing, and form a choir.Mathieu notices that the school is taking a turn for the better: The choir is improving rapidly with Morhange as its lead soloist, the children are happier, the faculty less stiff, and even Rachin begins to loosen up, playing with the boys and practicing flying a paper airplane. Mathieu and the school's caretaker rebel by taking the boys into the woods to enjoy the sunshine. While they are out, Mondain returns and sets fire to the roof. Mathieu is fired for breaking the rules, even though he saved the boys' lives. As he leaves, the boys, who are forbidden to say goodbye, throw messages to him on paper planes out of the window. Touched, he waves farewell. The final scene shows Mathieu waiting for his bus after being fired. As he boards the bus he looks back and finds Pépinot running after him, insisting that he come too. Initially Mathieu refuses, saying that this is not allowed. But he gives in and they board the bus together, and we hear Mathieu narrating, saying that Pépinot had got his dream, for Mathieu and he left on a Saturday.