A particularly unpleasant murder, that of a very old woman in a housing project, rocks the town of Lafferton. The murderer has left a distinctive "sign" on the body and at the scene of the crime. A couple of weeks later, a similar murder occurs, and a month or so later, so does another. Initial investigations discover that the mysterious "sign" left on the body was the calling card of a suspect who was charged with several murders in the northwest of the country, tried but acquitted on the grounds of insufficient evidence. All indications suggest that this person has simply vanished. Or is he right under their noses? Simon Serrailler is obliged to delve deeper and scratch out answers.