Following his dream of becoming a musketeer, D’Artagnan (Logan Lerman) leaves for Paris, where he finds Athos (Matthew Macfadyen), Aramis (Luke Evans) and Porthos (Ray Stevenson) in miserable jobs, looking for a cause to clear his name. Three years ago, after stealing a secret project from a vault Venetian, they were betrayed by their partner Milady (Milla Jojovich), who sold the Duke of Buckingham Plan (Orlando Bloom).
Meanwhile, the evil Richelieu (Christoph Waltz) devises a plan to dethrone King Louis (Freddie Fox). With double agents Milady cardinal framed his Queen Anne (Juno Temple) an affair with Buckingham, hoping that Louis will believe the lie. In his view, things are simple: the queen will be condemned, England will be provoked to war, people will want a strong leader and he will become the new king of France.
To protect France from these machinations, D’Artagnan joins the musketeers and start the most dangerous mission, relying on the spirit of friendship that saved every time: all for one and one for all!