King Louis' estranged brother Gaston (newcomer Andre Flynn) returns to Paris, having previously been exiled from court. On arriving in the capital, he is involved in the brutal slaughter of a band of veteran soldiers at a tavern, and the Musketeers' loyalties are torn when the crown orders them to defend the villainous prince against recrimination. Meanwhile, as Louis welcomes his traitorous sibling back into the fold with open arms, Feron and Grimaud believe they may have found a kindred spirit.