With the king taking to his bed as dying the queen asks Aramis to help broker a peace treaty with her brother, the Spanish king and he sets out to meet the ambassador but is captured by Grimaud. The court then receives an ultimatum - the return of Aramis in exchange for captured Spanish soldiers, a ploy engineered by Grimaud, Gaston and the Duke of Lorraine to discredit the queen as an appeaser. Facing popular acrimony the other musketeers have the prisoners released and set out for the rendezvous, along with D'Artagnan's cousin Espoir, whom he has saved from the gallows and acquits himself well in the gun-battle. Aramis is freed but Grimaud escapes to use the queen's sponsorship of a literacy scheme for the poor against her and Athos's new love Sylvie whilst an old enemy of the musketeers returns to the court.

Treville takes controversial steps to protect the Dauphin as France's enemies draw closer. Will his secretive tactics drive the musketeers apart?