Set in the early 17th century kingdom of France, the opening instalment of Martin Bourboulon’s epic two-film production follows a spirited young swordsman, Charles D’Artagnan, on his journey from Gascony to Paris to join the King’s elite Musketeers of the Guard. Along the way, he narrowly escapes death whilst heroically saving a woman from being kidnapped. In his efforts to enlist, D’Artagnan manages to offend the sensibilities of three of the most formidable Musketeers in the ranks, Athos, Porthos, and Aramis.

But D'Artagnan soon wins them over, and his dedication to help his newfound friends and serve King Louis XIII will lead him not only into the path of the mysterious Milady de Winter and the Queen's consort Constance, but the heart of a conspiracy where the future of the nation itself is at stake.