Set in the 1660s and concerned with the early reign of Louis XIV, the novel has been called an "origins" story of the King, "a tale about the education of a young man who went on to rule for over 70 years and become one of France's most beloved monarchs."

After 35 years of loyal service, d'Artagnan resigns as lieutenant of the Musketeers as he perceives the young king Louis XIV as weak-willed.

In France, Cardinal Mazarin has died, leaving Louis to assume power with Jean-Baptiste Colbert as his finance minister.

Colbert has an intense hatred for his superior the king's Superintendent of Finances, Nicolas Fouquet, and tries to bring about his fall.

Louis persuades d'Artagnan to re-enter his service, and tasks him to investigate Belle Île, promising him a substantial salary and promotion to Captain of the King's Musketeers on his return.

D'Artagnan confirms that Belle Île is being fortified and the architect ostensibly in charge is Porthos, though the drawings show the handwriting of Aramis, who is now the bishop of Vannes.

Meanwhile, Aramis meets the governor of the Bastille M. de Baisemeaux, and learns of a secret prisoner who bears a striking resemblance to Louis XIV.

To avoid her new husband being jealous Henrietta suggests that the king choose a young lady at court to act as a smokescreen for their flirtation.

Through an elaborate subterfuge mounted by Aramis, Philippe replaces a prisoner due for release from the Bastille and escapes to Vaux.

While the king is still visiting Fouquet at Vaux, Aramis initiates the second half of his plan and abducts Louis, imprisoning him in the Bastille in Philippe's place.

Realising that his plot has unravelled, Aramis flees for Belle Île to escape the king's impending wrath, taking Porthos with him.

Louis imprisons Philippe once more, ordering that "he will cover his face with an iron visor" which he "cannot raise without peril of his life."

Athos and Raoul meet Aramis and Porthos who relate their predicament before receiving horses to aid their journey to Belle Île.

Despite Fouquet's refusal to go along with Aramis's plot, Louis orders d'Artagnan to arrest him, which he manages following an epic chase.

French academic Jean-Yves Tadié has argued that the beginning of King Louis XIV's personal rule is the novel's real subject.

[2] In his essay "On a Romance of Dumas's", author and critic Robert Louis Stevenson wrote that "it is in the character of D'Artagnan, that we must look for the spirit of morality, which is one of the main joys of its perusal, and sets it high above more popular rivals.

"[3] However, Arthur F. Davidson argues in Alexandre Dumas: His Life and Works that The Vicomte is truly the story of Porthos, whose character was informed by Dumas' own experiences and his father's: "The modern reader may draw back aghast at the six volumes of Le Vicomte de Bragelonne, but he will have missed the best part of the Musketeer cycle should he fail to read those pages which describe the end of Porthos.