Set in 17th century Paris, musketeers Athos, Porthos, Aramis and D’Artagnan are members of an elite band of soldiers who fight for what is just. They are heroes in the truest and most abiding sense – men that can be trusted an believed in to do the right thing, regardless of personal risk.
Young swordsman d'Artagnan arrives in Paris seeking the man responsible for killing his father – a quest that brings him into conflict with one of the king's guards. But as he quickly discovers, when you take on one Musketeer, you take on them all. It's soon back to business when the swashbuckling heroes are ordered to find a missing soldier who was carrying important letters on behalf of King Louis, while the dastardly Cardinal Richelieu plots to increase his political power.
Notorious criminal Vadim seeks to make life unbearable for the authorities that have imprisoned him. When he engineers a full-scale riot, it falls to the Musketeers to protect those whom he seeks to destroy.
The Musketeers are dispatched to Le Havre to collect the infamous merchant trader and explorer, Bonnaire and bring him back to Paris to be reprimanded for breaking France's trade treaty. This straightforward mission soon descends into a treacherous battle, as they must defeat Bonnaire's surprising number of enemies. Athos is forced to confront his past, which threatens to engulf him.
When Aramis's old friend and former musketeer, Marsac, unexpectedly returns to Paris, the musketeers are thrown into turmoil, fully aware that they should report him for desertion. His appearance coincides with the royal visit of the King's beloved sister and her husband, the Duke of Savoy, whom the musketeers must protect. Marsac believes he finally knows the truth behind the infamous massacre which killed his troop, and wants Aramis's help to prove it.
Porthos wakes up from his drunken birthday celebrations with no memory of the night before, and with a dead body by his side. After being unjustly sentenced to death, he is abducted to the dangerous Court of Miracles. In their investigation to prove his innocence, the Musketeers uncover a tangled web of divided loyalties and greed, and they risk their lives to infiltrate the unruly slums of the Court of Miracles before it's too late.
Aramis and D’Artagnan have troubles transporting a young woman and her baby from a village outside Paris. The King’s royal hunting party is disrupted by the appearance of Louis’ banished mother seeking royal protection from an unknown assassin.
Following the tragic death of a young girl underneath the royal carriage, The Musketeers’ investigations into her missing friend lead them into the world of a high-born and enlightened woman. The Musketeers are forced to put aside their animosity towards the Cardinal when his life is placed in danger and they must rescue this extraordinary woman.
The Musketeers are tasked with bringing the fearsome Labarge, a regional intendant under arrest for the murder of two Musketeers, to Paris. The Red Guards, resentful of the Musketeers' handling of him, initiate a vicious fight between the two regiments. Fed up with the disruptive rivalry between the Musketeers and the Red Guards, the King calls a contest to prove which group is the stronger. D'Artagnan is determined to be chosen to fight so that he can prove himself worthy to be a Musketeer.
Queen Anne’s taking of the waters is cut short when her life is put in mortal danger. King Louis dines with wealthy German banker Count Mellendorf, who is looking for a French match for his beautiful daughter. As the Musketeers try to spirit Anne back to Paris, they’re forced to seek refuge in a fortified convent, where Aramis comes face to face with his past.
Athos takes a woman hostage in the square and the Musketeers are amazed to discover he is threatening none other than Milady. Athos is furious when he finds out that D’Artagnan knows her, testing their friendship to its limits. The Cardinal, fearful the Musketeers will prove he masterminded the attempt on the Queen’s life, compels Milady to kill them by any means. Milady has no choice but to revisit her dark past and in doing so puts Constance into danger. The Musketeers must use all their wits and courage to outsmart her and save Constance.