A bloody African statuette is found near the lifeless body of Adrien Dorval, a 65-year-old retired engineer who had opened a pottery workshop. The medical examiner notes that the victim's torso was slashed post-mortem. Strangely enough, the statuette is not the murder weapon. Adrien Dorval was actually killed with a clay roller found in a trash can near the crime scene. The investigation gradually puts Astrid and Raphaëlle on the trail of a Machiavellian revenge. The police officer and the librarian are in for a surprise. Raphaëlle also fears being shelved.