Les Trois mousquetaires: La vengeance de Milady (1961)
Directed by Bernard Borderie

Film Synopsis

In 1620s France, the powerful Cardinal Richelieu conspires with the evil Milady de Winter to avenge the affront inflicted upon them by their mortal enemy d'Artagnan.  They have their opportunity when the brave musketeer returns with a message for the queen, written to her by her secret lover, the Duke of Buckingham.  Realising that the letter may contain irrefutable proof of the queen's treachery, Richelieu determines to get his hands on it, by all the means he has at his disposal.  To that end, he arranges for d'Artagnan to be arrested and thrown into prison.  The young swordsman is expecting to be rescued by his loyal friends Athos, Porthos and Aramis, so he is understandably surprised to be saved from execution by his worst enemy, Milady.

By exercising her feminine charms and guile, Milady plans to seduce d'Artagnan and thereby get him to betray his queen.  Meanwhile, the musketeer's precious sweetheart Constance Bonacieux has been imprisoned by the Count of Rochefort in a convent, where he resorts to torture to make her talk.  With the help of his three comrades-in-arms, d'Artagnan manages to escape the vengeful clutches of Milady, and they then turn their attention to rescuing the unfortunate Constance.  It is at this juncture that a dreadful connection between Athos and Milady is discovered...