After discovering his older sister has been inexplicably murdered, D’Eon de Beaumont joins the French secret police–which has been investigating the disappearances of numerous young women–in hopes of solving the mystery of her death.

D’Eon’s battle against Vorontsov is finally finished, with Lia dealing the final blow. The Four Musketeers follow Robespierre to London.

After D’Eon speaks to the Queen about two souls existing together in one vessel and Durand is released, the Four Musketeers head for Medmenham Abbey.