While working on the Palais des Papes workers discover a 14th century secret chamber. Inside is a woman's skeleton. The autopsy shows that the victim is a childhood friend of the investigator handling the case. A second body is soon found.

During construction work at the library of the Palais des Papes, workers discover a secret vault, built in the 14th century to protect Pope Benedict XIII. They also make a macabre discovery: a woman's skeleton. Laurence Ravel, the Avignon police chief, takes charge of the case, while her 25-year-old niece, Julie Ravel, joins the team. The skeleton found in the secret vault turns out to be that of Isabelle Blanchard, a childhood friend of Laurence. Then, the day after Julie's arrival, a second body is found, dreadfully mutilated, in the Chapel of the Penitents. And this one is another childhood friend of Laurence: Pascal Ledoux. Are the murders linked? What could be the connection to this bunch of high-school pals? Laurence and Julie will have to delve deeply into the terrible history of the Inquisition, but also into their own histories.—Happy_Evil_Dude