One morning, Frédéric Leprince, student of the school of peacekeepers and son of a commissioner, is found dead, a weapon in his right hand. Commander Anne Voreppe and Captain Chrystel Chesnot are in charge of the investigation. Émilie, sister of the victim and also a student, does not believe in the thesis of suicide. By questioning her, Chesnot discovers that the young woman is harassed by Sergeant Dangro as the captain was when she herself was a student in this school. The autopsy of the victim's body soon confirms the murder theory.