Having honed his swordsmanship with lessons from his father, the young and naive rural lad, D'Artagnan, arrives in the vibrant city of Paris. With him, he carries a letter from his father, Joss Ackland, which introduces him to Captain Treville, the leader of the King’s Musketeers. D'Artagnan's father has imparted a secret thrust technique—a move reserved solely for the gravest of dangers—and entrusted his son with 15 crowns to facilitate his expenses. Additionally, he cautions D'Artagnan to be wary of the influential Cardinal, who rules over the kingdom in the shadows, manipulating the King.
Eager to join the ranks of the King's Musketeers, D'Artagnan faces the hurdles of city life, leading to a series of unfortunate mishaps. His journey takes a sharp turn when he encounters the nefarious Comte De Rochefort, an agent of Cardinal Richelieu. During this clash, D'Artagnan suffers humiliations; he is knocked unconscious, robbed, and ultimately loses his father's sword in the struggle. Following this encounter, Rochefort’s men send D'Artagnan away, having pilfered his money and left him disgraced.
Arriving at the barracks of the King's Musketeers, D'Artagnan presents himself to Captain Treville. Observing the remains of the broken sword, Treville realizes D'Artagnan has not yet earned his place as a warrior, instructing him to gain experience through service in campaigns or with the general guards. In his quest, D'Artagnan crosses paths with three storied Musketeers: Athos, Porthos, and Aramis. A miscommunication leads to each of them challenging D'Artagnan to duels—one after another—over perceived insults.
Just as the first duel between D'Artagnan and Athos is set to commence, Jussac arrives with additional guards loyal to the Cardinal, accusing the Musketeers of defying the Cardinal's proclamations. In a thrilling twist, D'Artagnan chooses to side with the Musketeers during the ensuing street brawl, proving himself invaluable by helping to vanquish the Cardinal’s guards. In this moment of solidarity, Athos shares the Musketeers' famed motto: "One for all, and all for one."
Recognizing the newfound bond, Athos shares his winnings from the skirmish with D'Artagnan, providing him means to rent a room and acquire new attire, thus sealing their alliance against the Cardinal's growing ambitions to dominate the throne of King Louis XIII. D'Artagnan dwells at a shabby lodgings but is smitten by the charm of Constance Bonacieux, the landlord's alluring wife who also serves as the Queen’s dressmaker. To assist him, Planchet is taken on as D'Artagnan’s servant.
Meanwhile, the enigmatic Duke of Buckingham, the Queen’s former lover, arrives from England, prompting Cardinal Richelieu to alert the King. Fearing that the Duke's presence could threaten the Queen's honor, the King orders his arrest. Richelieu deceives the King by claiming that the Duke’s reputation is untainted. Amid this tension, Rochefort menaces Constance and her spouse at their residence, leading Constance to seek refuge with D'Artagnan, pleading for help to protect the Queen from the Cardinal's schemes.
In their meeting, romance flares between D'Artagnan and Constance. However, this moment is bittersweet as Constance attempts to aid the Duke in secret meetings with the Queen. Complications arise as D'Artagnan discovers Constance's involvement with the Duke. The Queen eventually insists on ceasing their encounters to preserve her dignity, knowing the Cardinal is privy to their liaisons. Against a backdrop of royal intrigue, the Duke is prepared to escalate tensions for love, prompting a series of events that bring D'Artagnan joy and peril alike.
When the Cardinal learns of their correspondence, he strategically suggests throwing a grand ball, encouraging the Queen to display her priceless necklace as bait. The plot thickens as the cunning Milady De Winter, in service of the Cardinal, seduces the Duke to pilfer two diamonds from the Queen's necklace. Meanwhile, Constance vows to send a trustworthy message to England, seeking D'Artagnan's aid once again to retrieve the diamonds.
Together with the three Musketeers, D'Artagnan embarks on an adventure filled with treachery and heroics. They face multiple ambushes from the Cardinal's men, and it becomes a race against time to make it to the Duke. Upon learning of the missing jewels, the noble Duke arranges for exquisite replacements at an outrageous cost and gifts D'Artagnan with a swift vessel and his own sword for the mission’s success.
Resilience and camaraderie prevail when D'Artagnan and the Musketeers manage to return the completed necklace to the Queen just in time, thwarting the Cardinal’s machinations. Following these harrowing escapades, Captain Treville triumphantly welcomes D'Artagnan into the Musketeers of the King's Guard, his journey culminating in new friendships and budding romance, setting the stage for further adventures. The future remains shrouded in possibilities as D'Artagnan's interactions with Milady De Winter deepen, weaving a tale rich with honor, loyalty, and relentless pursuit of justice.
