A third girl has been murdered in the middle of the festive season. Superintendent Rousseau is not convinced by the serial-killer hypothesis which the newspapers keep churning out.

Superintendent Rousseau of the murder squad, and his deputy Mariella De Luca, a young profiler, lead the investigation of a severed head found inside the Catacombs in Paris: the victim is Maximilien Müller, a famous contemporary artist known for his sulfurous past.

A teenager's butchered body is found by the Seine. Superintendent Rousseau, haunted by old demons, hands control of the investigation to his deputy, Mariella De Luca, who must also deal with the girl's mother, Katia.

In the doorway of the neighbourhood's most-renowned bakery, a young student collapses, shot dead. It's an inexplicable murder: no weapon, no suspect, nothing in the victim's past to provide any lead.