It is the start of the summer holidays for Quinquin and it is also the start of a local killing spree after a woman is found chopped up and fed to a cow, who is found dead in an old bunker.

Van der Weyden and Carpentier discover that the two victims were lovers. Meanwhile, Quinquin and his friends follow the case with an investigation of their own.

The forensic vet warns Var der Weyden that the cows were suffering from mad cow disease. Meanwhile, Quinquin inadvertently makes a discovery that solves part of the mystery.

Mohamed becomes insane after being humiliated by Ève's sister. Meanwhile, Var der Weyden and Carpentier face new and atrocious murderers as they get closer to solving the case.