The Four Musketeers: Milady's Revenge (1974) on Netflix

D'Artagnan has become a Musketeer. Protestants hold La Rochelle, and the Queen loves Buckingham, who'll soon send ships to support the rebels. Richelieu enlists Rochefort to kidnap Constance, the Queen's go-between and D'Artagnan's love. The Cardinal uses the wily, amoral Milady de Winter to distract D'Artagnan. But soon, she is D'Artagnan's sworn enemy, and she has an unfortunate history with Athos as well. Milady goes to England to dispatch Buckingham; the Musketeers fight the rebels. Milady, with Rochefort's help, then turns to her personal agenda. Can D'Artagnan save Constance, defeat Rochefort, slip de Winter's ire, and stay free of the Cardinal? All for one, one for all.