In the city of Lyon, despite the police's best efforts, an elusive assassin is targeting ordinary citizens. They all share one thing in common: suspected of serious crimes, they have all managed to escape justice. In the press and among some of the public, a name is circulating: "The Vigilante." A local police commissioner and a somewhat self-important Parisian profiler, Marie Sainz and Claire Legendre, team up to try and unmask and stop this overconfident killer.