During the reign of French King Louis XIV, royal troops kidnap Philippe, a young commoner who bears a striking resemblance to the king, and incarcerate him, along with his four guardians, known as the sword-fighting musketeers D’Artagnan, Athos, Aramis and Porthos. Elsewhere, Princess Marie-Therese of Spain sails to France for her diplomatic marriage to Louis XIV, which is meant to put an end to the ongoing war between their two countries, but she has doubts about the philandering king who is unpopular among the French people. At the Bastille prison in Paris, an iron mask is forged for Philippe to ensure that no one will see his familiar face. Also, the soldiers who already have caught sight of him are executed by order of the cunning Fouquet, the king’s chief minister. Meanwhile at the palace, Louis explains to his mistress, Madame de la Valliere, that he and Fouquet will stage an assassination tomorrow. While Louis remains hidden, the double will pose as the king and greet Marie-Therese at the arrival dock. In front of the public, the look-alike will be murdered. Afterwards, the real king will miraculously reappear, signifying to the French people that he has immortal powers, and thereby assuring their loyalty. Through a secret passageway underneath the Bastille, Fouquet leads the prisoner in the iron mask to the king’s private chambers and tells him that if he follows instructions, his fellow musketeers will be released unharmed. When Philippe arrives at the dock dressed as Louis XIV, Colbert, a high-ranking court official who is loyal to the musketeers, recognizes the masquerade and warns the young man to be cautious. As Philippe slowly walks to the end of the dock to await Marie-Therese’s boat, he sees smoke rising from the planks and dives into the water, narrowly escaping an explosion. After swimming to shore, he grabs a sword and fends off another assassination attempt. While the crowd of onlookers cheer their brave king, Colbert advises Philippe to use his power to decree that all prisoners are to be freed from the Bastille immediately. In the meantime, Louis prepares to greet the public as the resurrected monarch, until Fouquet stops him with the shocking news that the double is still alive. After witnessing the heroics at the dock, Marie-Therese is pleasantly surprised by the king. Later that night, during a fireworks show welcoming the future Queen, Philippe and Marie-Therese observe an attraction between each other. Before Philippe disappears to rejoin the musketeers, he promises Marie-Therese that he will return soon and kisses her. As soon as Louis XIV resumes his place at the palace, he requests that Marie-Therese sign over her dowry before the wedding, which is not customary, but advantageous to his nearly bankrupt estate. She is uncomfortable with the arrangement and also perplexed by the king’s abrupt change in personality from the previous night. In the countryside, Philippe and the musketeers retreat to the basement of an inn, run by their trusted friend, Bernard. Unaware until now of resembling the king, Philippe inquires about his background, and the musketeers reveal that he is the twin brother of Louis. At the birth, the royal family knew that twins would complicate inheritance to the throne, so one of the boys was committed to the protection of the musketeers, who were held in high esteem by the king at that time. D’Artagnan says that no one knows who was first born. To the amusement of the elder musketeers, Philippe contemplates himself as king, if only to rescue the lovely Marie-Therese. Meanwhile, the king’s mother, Queen Anne, confirms the same news to Louis and urges him not to harm his twin brother. Elsewhere, Marie-Therese tries to flee France and her arranged marriage. Concerned about the political consequences, Colbert convinces the musketeers to intercept her carriage ahead of Louis’ troops. While D’Artagnan, Athos, Aramis and Porthos fend off the king’s soldiers, Philippe carries Marie-Therese away on his horse. During the getaway, Philippe explains his true identity to the Spanish princess, and the couple spend a romantic night at a secluded inn. However, their whereabouts are soon discovered, and Philippe is once again imprisoned in the iron mask while Marie-Therese is returned to the king’s court. With the advice of Colbert, the princess undertakes a scheme to dethrone Louis. The night before the wedding, Marie-Therese flirts with the king and drugs his wine while the four musketeers slip into the palace. As soon as Louis loses consciousness, the musketeers carry his body to the Bastille through the secret passageway. There, they release Philippe and lock the king in the iron mask. When Louis wakes in the cell and screams that he is the real king, no one believes him, including Fouquet. The next day, Philippe, disguised as the king, walks down the aisle for his wedding to Marie-Therese. Through an informant, Fouquet learns that Aramis and Porthos have seized command of the Bastille, which means that the man in the iron mask is Louis XIV, after all. He organizes a takeover of the prison by a group of rogue fighters and frees King Louis. During the conflict, Porthos and Aramis are mortally wounded, but before dying, Porthos staggers into the cathedral and interrupts the wedding to warn Philippe and the other two musketeers. In the secret passageway, Philippe and D’Artagnan intercept the king and Fouquet. The experienced swordsman D’Artagnan kills Fouquet, but as the twin brothers duel, they tumble off a shaky bridge into the underground moat. Louis is swept away by the swift current, while Philippe is rescued by D’Artagnan. When Philippe returns to the altar dressed as the king, Madame de la Valliere cries out that he is not Louis of France. In front of the congregation, Queen Anne proclaims that this man is her son, and the royal wedding between Philippe and Marie-Therese proceeds.