There have been many adaptations of The Three Musketeers over the decades, some good, some dreadful. This particular adaptation, the first I ever saw, is...a mixed bag.
The film follows the original novel pretty closely. Our hero, d'Artagnan (Gene Kelly), is leaving his native Gascony for Paris to join the famed musketeers. D'Artagnan, however, has a swelled head and a short fuse. This not only gets him in trouble with the Comte de Rochefort (Ian Keith, who also played Rochefort in a 1935 adaptation), but also three of the best musketeers in the regiment - Athos (Van Heflin), Porthos (Gig Young), and Aramis (Robert Coote). He ends up getting challenged to duels by all three musketeers in a matter of minutes, but they become friends after they fight of a group of Prime Minister Richelieu's men together. Not long afterwards, he distinguishes himself again when he rescues Constance Bonacieux (June Allyson) from a gang of Richeliue's thugs. Constance turns out to be a maid to Queen Anne of Austria (Angela Lansbury), who is having an affair with the English Duke of Buckingham (John Sutton). As a parting gift, the queen has given Buckingham a casket of twelve diamond studs to remember her by. However, the queen is a pawn in the power struggle between King Louis XIII (Frank Morgan) and Prime Minister Richelieu (Vincent Price). Richelieu dispatches Milady de Winter (Lana Turner) to steal two of the diamonds to use as proof of Anne's infidelity, provoking a war with England. Constance turns to d'Artagnan, and his three new friends join his desperate journey to England to prevent a war.