During the 18th century in Paris, a coffin carrying the lifeless body of Lia de Beaumont, a noblewoman and spy of King Louis XV, is discovered floating on the Seine River. Her younger brother, Charles d'Eon, who has just been knighted, is convinced that the recent disappearances in the city are related to his sister's untimely demise. Thirsty for justice, d'Eon joins the secret police to help solve the case. As they delve deeper into their investigation, they unravel a sinister plot concocted by members of the French and Russian nobility with the backing of a cult. It becomes clear to d'Eon that Lia's death may have been linked to her discovery of this conspiracy while on a mission. On the fateful night that the secret police are set to arrest the Duke of Orléans as a suspect, a Gargoyle, a demonic creature, appears out of nowhere and attacks the group, leaving only one survivor who has been transformed into another Gargoyle. d'Eon valiantly attempts to save the survivor, but to no avail. In the midst of the chaos, Lia's spirit takes possession of d'Eon's body and defeats the Gargoyle herself. After this encounter, d'Eon realizes that he needs allies to unravel the mystery of this supernatural conspiracy fully.