When Monsieur Crauqual, the supervisor, is found hanging, all wonder why this rather rich person decided to kill himself. And when a pupil is found hanging too, François and his friends decide to investigate. They are certain there is a killer within the walls of Collège François 1er and determined to prevent him from going on running wild.

Alice, an unhappy young woman in the household, is the mother of a little boy, Pierre. She falls in love with a young doctor and plans to run away with him and his son. Finally, not considering the right to deprive Pierre of his father, she gives up. Twenty years pass, Pierre has grown up, he suspects his little brother, Jean, of just being his half-brother. His suspicions gnaw at him, his mother confesses to him her past fault. Faced with this confession, Pierre will abandon the one who sacrificed her life for him.