In 1662, the Kingdom of France faces bankruptcy from King Louis XIV's wars against the Dutch Republic, which has left the country's agriculture impeded by a heavy tax burden and forced the citizens to live on rotten food. Though the country appears to be on the verge of a revolution, Louis continues to spend his time preparing for war and seducing countless women. The three musketeers have gone their separate ways; Aramis is now an aging priest, Porthos has become a philandering drunk, and Athos is retired and living with his only son, Raoul, who aspires to join the Musketeers. Only D'Artagnan has remained with the Musketeers, now serving as their Captain.
At a festival, Aramis learns that the Jesuit order has declared Louis's wars unjust and the source of public hunger and outrage. Louis personally instructs Aramis to secretly hunt down and kill the Jesuit leader. Also in attendance are Raoul and Christine Bellefort, the girl Raoul is in love with and plans to propose to. Louis immediately sets his sights on Christine, but faithful to Raoul, she resists his affections. A Jesuit assassin attempts to kill Louis but is killed by D'Artagnan instead. Louis immediately plots to seduce Christine by having Raoul sent to the battlefront. D'Artagnan visits Athos to warn him of the danger Raoul faces. But then Raoul arrives and informs his father he has been recalled to his regiment because he believes Louis desires Christine. Raoul nevertheless resolves to go immediately because he will not risk making Christine a widow nor consider himself a coward. Athos angrily warns D'Artagnan that if Raoul is harmed, then Louis will become his enemy. D'Artagnan tells Athos he will personally speak to Louis about Raoul.
An angry crowd from Paris attacks the Musketeers when they are fed rotten food, but D'Artagnan calms the crowd and says he will personally speak to Louis about public hunger. Louis assures D'Artagnan he will deal with the matter, and that Raoul will return soon from the war. Instead, Louis orders his chief adviser Pierre executed for distributing the rotten food (despite the fact that Louis earlier ordered him to do so), and orders that all rioters are to be shot from now on. Raoul joins the war and is killed at the battlefront by cannon fire. Upon learning of his son's death, Athos attempts to kill Louis but is stopped by D'Artagnan, and goes into exile. Louis invites Christine to the royal palace and coerces her into sex by pretending to care for her mourning and by promising to have his personal doctor treat her sick mother and sister and has them sent to recover at his country estate.
Aramis summons Porthos, Athos and D'Artagnan for a secret meeting in which he reveals that he himself is the Jesuits' leader and has a plan to depose Louis. Athos and Porthos agree, but D'Artagnan refuses to cooperate citing his oath of honor cannot be removed or betrayed. Athos angrily confronts D'Artagnan over his devotion and loyalty to Louis, but D'Artagnan still refuses to join their plot. Athos brands him a traitor and threatens him with death should they ever meet again.