In the turbulent France of 1678, Hortense Mancini, Duchesse Mazarine takes on the disguise of a King's Musketeer to pursue her love affair with Anne Lennard, Countess of Sussex. She crosses paths with a true Musketeer, and with Aphra Behn, English playwright and spy, both seeking to retrieve letters between the kings of France and England that could prove ruinous. Every disguise and plan is threatened by the arrival of a young woman who seeks to gain fame by besting a Musketeer in a duel--and now she has a chance to challenge two of them!