En 1948 Clément Mathieu, profesor de música desempleado, acepta un puesto como profesor vigilante en un internado de reeducación de menores. El sistema represivo aplicado por el director conmociona a Mathieu. Enseñándoles música y canto coral a estos niños tan difíciles, Mathieu transformará sus vidas cotidianas.
Commissioner Malaise investigates a strange crime: a mannequin, stolen from the window of a tailor, is found stabbed... But his face of wax has the features of a certain Gilbert, who died a year earlier in a family, all of whose members will become more or less suspicious to the Commissioner. He thinks that, in spite of Dr. Furnelle's conclusions, Gilbert's death was not natural. But finding the cause of death and the identity of the possible culprit will require more than a mere intuition.
