D’Artagnan, on a quest to rescue the abducted Constance, runs into the mysterious Milady de Winter again. The tension between the Catholics and the Protestants finally escalates, as the king declares war — forcing the now four musketeers into battle. But as the war goes on, they are tested physically, mentally and emotionally.

D’Artagnan, a spirited young Gascon, is left for dead after trying to save a noblewoman from being kidnapped. Once in Paris, he tries by all means to find his attackers, unaware that his quest will lead him to the very heart of a war where the future of France is at stake. Aided by King’s Musketeers Athos, Porthos and Aramis, he faces the machinations of villainous Cardinal Richelieu and Milady de Winter, while falling in love with Constance, the Queen’s confidante.

The government is asking Eiffel to design something spectacular for the 1889 Paris World Fair, but Eiffel simply wants to design the subway. Suddenly, everything changes when Eiffel crosses paths with a mysterious woman from his past.