Still trapped in the time of the Three Musketeers, Rebecca is mistaken for Madame D'Urfe, an assassin hired to kill King Louis XIII. Jules and Phileas must persuade the Three Musketeers to reunite to rescue Rebecca, and save the King by defeating Richelieu.

While investigating a country priest's murder, Jules is lured to a secret base of the League of Darkness, where they are creating a flying ship called the Prometheus. Jules accepts a commission at the behest of the ship's beautiful commander, unaware of the League's true purpose.