When a decapitated horse appears suspended on the top of a cable car, Commandants Martin Servaz and Irene Ziegler team up to investigate the mystery behind the cruel act.

The investigation leads Servaz to discover Hirtmann's hair in the dead horse's blood; at the Warnier center, Diane pays a visit to Hirtmann and reveals her true intentions.

The discovery of Garaudy's emasculated corpse leads to fears of new murders, as Servaz and Ziegler discover the trail of revenge relates back to sexual adolescent crimes committed 15 years earlier.

Servaz and Ziegler's investigation leads them to the murder of Perrot, a close friend of Garaudy; in a rush to avoid another death, the two discover a string of connections between Garaudy and Perrot to the current mayor of Saint-Martin, Chaperon.

After Chaperon's death, Servaz and Ziegler discover video footage of Chaperon, Perrot, Garaudy and two other unknown predators; Diane learns of Servaz's role in her sister's death.

Servaz fears a repeat of history when Diane gets captured, just like her sister Fabienne 10 years earlier; Servaz races against time to reveal the true culprit before any more people die.