France is in turmoil as the young King Louis XIV (Leonardo Dicaprio) cares nothing for his people or their well-being. Former, aging Musketeers Athos, Porthos and Aramis (John Malkovich, Gerard Depardieu and Jeremy Irons) concoct a plan to replace the evil Louis with a substitute, the mysterious Man in the Iron Mask (The King's banished twin bother Phillip, also played by DiCaprio), who they hope will prove to be a better king.
The problem lies in the devotion of their friend, D'Artagnan (Gabriel Byrne), who is the Captain of the King's Musketeers, to the selfish monarch. To succeed in their plot, the musketeers will have to either turn D'Artagnan against the king, or fool him into believing Phillip is Louis. They free Phillip from his prison, and train him in the ways of the royal court. They decide to kidnap Louis and replace him with Phillip at a masque.