It has been many years since Aramis, Athos, Porthos and d'Artagnan fought together as the bravest and best of the King's Royal Guards, the Musketeers. Athos (John Malkovich) lives a simple life raising his son Raoul. Porthos (Gerard Depardieu), though thicker and older, still eats lustily of life, though he misses the great battles of the past. Aramis (Jeremy Irons) has followed his faith and become a priest. Only d'Artagnan still serves the King as Captain of the Musketeers.
It is 1660 and France is starving. Louis XIII, the great King whose throne the Musketeers served has died and been succeeded by his arrogant and cruel heir, King Louis XIV (Leonardo DiCaprio) ... while at the Bastille a mysterious prisoner has lived for nearly a decade encased in an iron mask. To save a nation, the Musketeers must reunite and embark on their most dangerous mission ever: to free the prisoner and unlock the secret of his identity.