The musketeers are to help with security during the diplomatic visit to sign a crucial treaty with France, rather then Spain, of the duke of strategic savoy and his wife, king Louis's sister, with their bright prince Louis Amadeus. Aramis is shocked to have to apprehend for an attempt at the duke's life his former comrade in arms Marsac, who swears he deserted to avenge the murder of two dozen of their comrades five years ago by the duke. Still he makes D'Artagnan put up the runaway with far from pleased Constance, while the friends look into Marsac's claim of proof, the duke's allegedly murdered former trusted chancellor Cluzet, who is indeed in the cardinal's secret prison. Marsac kills the only witness after he confirms part of the story and claims that musketeers captain Treville supervised the murders, which even Aramis finds almost unbearable to consider, yet must check upon to know which is France's true interest. The impetuous duke and his wife stir further trouble, even a duel.
—KGF Vissers