D'Artagnan, the main character, goes to Paris in hopes of joining the king's elite guards called the musketeers.
D'Artagnan manages to insult the three best musketeers. They meet up one day to duel, but beat up some other guards instead. They soon become friends.
Milady and Richelieu scheme to give the church more power. They tell the king they should have a ball in ten days, though they want it to belittle the queen.
The two invite Buckingham to get with the queen, but she doesn't like him. She does however, give him 12 jewels. These jewels are needed for the ball, but she doesn't know there's a ball yet. When she does find out, she sends the four musketeers off to get them back.
Milady beats them there and kills Buckingham but doesn't get the jewels. So they race back and fix the belittling problem, by returning the jewels.
I am dead
The four end up catching Milady, try her, and she is sentenced to death. But to stop them from "winning" she kills herself.