Porthos uncovers the truth about his parentage and demands answers from his new-found father. As he learns more about his past, Porthos questions his place in the Musketeers regiment. However, the Musketeers have suspicions about Porthos' new family, wondering whether he should trust them. Can they save Porthos from the dangers that lie ahead, and where do his true loyalties lie?

The Musketeers must risk everything to save France from Rochefort's treacherous plan. While Porthos seeks to lure the Spanish spymaster to Paris to prove Rochefort's betrayal to the King, Athos and d'Artagnan must save Constance from certain death. However will they be able to protect Aramis and the Queen before Rochefort gets to them first? The fate of France and their closest comrades lies in the Musketeers' hands.