After being left for dead, D'Artagnan travels to Paris to track down his assailants, which brings him into a bitter conflict that threatens France's future and has him join forces with the King's three musketeers, Athos, Porthos, and Aramis.
D'Artagnan is forced to cooperate with Milady in order to rescue Constance from the hands of her kidnappers, and with the declaration of war a secret from the past is revealed that threatens to break up old alliances.