(My review on goodreads)
As others have noted, the commissaire Adamsberg series is enjoyable mostly for the characters: Adamsberg, Veyrenc, Danglard, Retancourt, and a couple others. Other aspects of the series, and this novel, not so great. Let me explain.
First, every one of the books in this series has a supernatural element, for no good reason. For example, in A Climate of Fear the supernatural being is called the afturganga, a sort of invisible Icelandic thingus that is able to invade thoughts from a distance and yada yada yada. Absolutely not needed for the story - all the afturganga tricks could as easily have occurred without any supernatural intervention.
Second, there is always at least one, usually more, thrilling action scenes from which Adamsberg has a narrow escape, sometimes with grave injury. I don´t think these add much to the novels (though they may be a not-so-subtle attempt to attract a Hollywood producer). In this novel Adamsberg has a shoot-out with the serial killer, shortly after a violent encounter with the afturganga. Yawn.
Despite my objections this is an enjoyable read, overall, mostly for the Adamsberg, Danglard, Veyrenc, Lucio conversations. It scratches an itch, you might say.