Set in France in the 1600s. Young, dashing swordsman D'Artagnan hooks up with three of the King's Musketeers - Athos, Porthos, and Aramis - and becomes embroiled in an effort to foil a despicable plot against the Queen being masterminded by the evil Cardinal Richelieu and the notorious Countess De Winter. There is much in the way of adventure and derring-do. Last I checked, you can read it here:

http://www.hoboes.com/html/FireBlade/Dumas/Musketeers/

If you enjoyed this book you might also like Steven Brust's brilliant tribute to it, The Phoenix Guards. Oh! And also check out Rafael Sabatini's Captain Blood.