The torso has finally been identified: the victim was a policeman, a member of Bac Seine-Saint-Denis. On the spot, Gilou and Laure find the Commissioner Herville, their former superior. He informs them that a survey of the IGPN, investigated by Judge Roban, targeted the deceased's team. In another case, the mysterious death of Nicolas, the magistrate discovers that the young man and his roommate were paying off their charms. The trial of Thomas Weber, the son of a famous surgeon, begins.