At the top of a cable car in the Pyrenees, the body of a decapitated horse is discovered. Captains Servaz and Ziegler are entrusted with this highly complex investigation. A few miles away, in a high-security prison, psychiatrist Diane Berg begins psychotherapy sessions with Julian Hirtmann, a dangerous serial killer arrested years before by Captain Servaz. What if this imprisoned man is involved in this macabre affair?