At dawn, suspended at the top of a cable car, a dismembered and decapitated horse is discovered. Captain Martin Servaz of the SRPJ of Toulouse is given the team survey with captain Irène Ziegler of the Gendarmerie de Saint-Martin. Meanwhile, young psychiatrist Diane Berg makes her debut at the Warnier center, a prison facility housing notably the dangerous serial killer Julian Hirtmann.
After finding a hair of Hirtmann bathed in the blood of the decapitated horse's head, Servaz collapses. In the center Warnier, Diane confronts for the first time Hirtmann, who succeeds in penetrating the true identity of the girl and the informal reason of its presence in the center.
After the discovery of a second murder, Servaz feared new ones. The investigation continues and brings to the surface an old case that had shaken the region fifteen years ago: the suicide of a gang of teenagers. Diane, meanwhile, is seeking information from Hirtmann; the only reason for his visit to the Warnier Center.
A third murder was discovered. Again Servaz and Ziegler arrived too late. They then plunge into the "suicides case", and try to establish the link between this "suicides case" and the previous murders.
Chaperon, the mayor of Saint-Martin, was killed in his turn. And the killer once again escaped from Servaz and Ziegler. They discover unsustainable videos featuring Chaperon, Perrot and Garaudy, as well as two other predators, tracking teenagers as wild beasts. Who are the two unknowns? Who could have decided to take revenge 15 years later? Diane eventually obtained from Hirtmann the place where her sister Fabienne was buried. Frightened by guilt, Servaz reveals his responsibility in the death of the latter.
Diane was abducted and sequestered, like her sister Fabienne ten years earlier. Will Captain Servaz save her? What price will it have to pay to prevent the story from repeating itself again?
