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.

The Four Musketeers defeat the gargoyles, only to discover they were being controlled by a man. They follow him back to his masters and realize he was employed by several important French aristocrats.

King Louis XV gives the Four Musketeers a mission, and D’Eon asks Queen Marie why his sister’s soul has not passed on.

The Four Musketeers pursue Vorontsov until he finally arrives in St. Petersburg. Here D’Eon attempts to gain permission from Empress Elizabeta to operate in Russia.

Following the Empress’ death, Pyotr has become Emperor of Russia. Ekaterina, the woman who warned the Four Musketeers, steals the throne back from him with their help. The Four Musketeers continue to battle members of the Revolutionary Brethren.

Robespierre captures and interrogates Durand; D’Eon and the others attempt to rescue him.

Lia continues reciting Psalms until Teillagory calms her down. King Louis receives copies of Robert Wood’s documents.

Upon witnessing the deaths of the Queen and Anna, Robin shoots at the king, but Broglie protects him and allows him to escape. D'Eon sees another of Lia's memories of her and Maximilien, finding out that he had proposed to her and that she had agreed happily, and that Maximilien disliked the King for keeping him and Lia apart. Maximilien abandoned the King's orders for him to go to Russia, stealing the Royal Psalms and giving them to Lia for her to read instead. While she manages to read the Psalms, she wrote Maximilien a letter claiming that she was unable to do so and rejecting his love. Meanwhile, Maximilien approaches a now hateful Robin, commenting that Robin's ability to actually carry the Psalms is a sign that the Psalms want change to occur in France, and telling him to take revenge for his murdered friends. D'Eon is chased down by palace guards, but Lorenza kills them, and once free he visits Anna's coffin. He then sneaks into Broglie's room and forces him to bring him to the King's chambers. Lia then takes over, asking the King whether he was responsible for the deaths of Anna, Queen Marie, and Lia herself.

The orchestrator behind Lia’s murder explains everything, and all that D’Eon worked for comes to an end.