A monk is found murdered below the fort Royal on the St Marguerite Island outside Cannes. The infamous island that housed the Man with the iron mask. Who killed the monk and why? Camille and Harry cross paths once again, making Lea jealous. Harry's old friend Father Placid was a mentor to the dead monk, and Camille and Lea have to track down the victim's troubled past in order to find the answers. Harry is one step ahead but gets in over his head, having to rely on Camille's help to stay alive. Meanwhile her father's nemesis Julien Boire makes it even more personal by approaching Camille's sister Margaux. His warning to Camille is clear — stop digging or else.
