The Three Musketeers: D'Artagnan

On his way to Paris to join the Musketeers of the Guard, D'Artagnan, a young man from Gascony, is almost killed trying to stop a young noblewoman from being kidnapped by a group of armed men. In Paris, D'Artagnan visits Capitaine de Tréville, the commander of the musketeers, at its headquarters. Tréville, who knew D'Artagnan's late father, encourages him to start a military career as a cadet. Through a window, D'Artagnan sees one of the men who tried to kill him days earlier. As D'Artagnan rushes out of the building to confront him, he unintentionally offends—on three occasions—three musketeers: Athos, Porthos and Aramis, who demand satisfaction. D'Artagnan schedules a duel with each of them the same day.

As D'Artagnan prepares himself for the first duel, he realizes that Athos's seconds are Porthos and Aramis, who are astonished that the young Gascon intends to duel them all. As D'Artagnan and Athos begin the duel, Cardinal Richelieu's guards appear and attempt to arrest the musketeers and the Gascon for illegally dueling. Although they are vastly outnumbered, the four men win the battle. Although proud of his guards' victory over Cardinal's guards, King Louis XIII nevertheless upbraids the musketeers and warns them the next man caught dueling will be sent to the dungeon.

D'Artagnan becomes friends with the Three Musketeers. He discovers that Porthos is bisexual. He finds lodgings and falls in love at first sight with Constance Bonacieux, a sentiment which she eventually comes to reciprocate. She works for Queen Anne of France, King Louis' wife, who is secretly in love with the Englishman Duke of Buckingham. Cardinal Richelieu plots to demonstrate that Queen Anne is cheating on her husband, which would lead, according to Richelieu's plan, to her beheading.

The king's military and clerical advisers and his younger brother Gaston (Louis' heir presumptive and political rival) urge the king to fight Protestant rebels at their stronghold of La Rochelle. King Louis, conscious of the history of religious wars under his predecessors, refuses to authorize a war.

An unknown young woman is found dead and naked, with multiple stab wounds, in bed with Athos. Athos is falsely accused of murder and is sentenced to death by the King's court. D'Artagnan realizes it was the same young woman he tried to save from being kidnapped on his way to Paris. Seeing a chance to save Athos, the musketeers resolve to learn her identity. D'Artagnan goes to the House of Valcour to talk to a family they believe is connected to the woman. While there, he meets Milady who pretends to be a member of the Valcour family. When D'Artagnan recognizes that she is an impostor, Milady attempts to kill him, but D'Artagnan eludes her.

Athos is freed on the way to his execution by his younger brother, Benjamin, who is in hiding with his allies, leaders of Protestant rebels, Saint-Blancard and Brandicourt.

The king gives the queen a gift of diamonds, but she gives them to Lord Buckingham as a keepsake. The king hears rumors of the affair and demands that the queen wear the diamonds to his brother's wedding. Constance sends D'Artagnan to England to retrieve the diamonds from Buckingham. Milady, an agent of Cardinal Richelieu, steals the diamonds from Buckingham, but D'Artagnan chases after her and retrieves them. Milady jumps off a cliff to escape. D'Artagnan returns the jewels to Queen Anne just in time to save her honor.

At the wedding of Gaston, Duke of Orléans and Marie de Bourbon, Duchess of Montpensier, the Gaston-aligned plotters within the top ranks of French military join forces with the Protestant rebels, including Athos' brother, to try to assassinate the king, but Athos and the rest of the musketeers save him. The king pardons Athos and appoints D'Artagnan a lieutenant in the Musketeers.

At the film's ending, D'Artagnan is knocked unconscious in a dark street by one of the plotters' henchmen while trying to save Constance from being kidnapped.

In a mid-credits scene, Milady is seen speaking with Cardinal Richelieu. She mentions the problems the musketeers caused to her mission.