The one that comes to mind, the one that will always come to mind is The Scarlet Pimpernel. This was (and still is) my favorite book of all time when I was in middle school and I can't tell you how many times I've read it. Set during the the first Revolution, The Scarlet Pimpernel is a combination Zorro and Robin Hood, an Englishman who disguises himself in order to save aristocrats from the guillotine. Dashing and daring, no one knows who he is but all of London admire him while all of France curse his name. A former actress from Paris, Marguerite St. Just - now Lady Blakeney, is blackmailed into trying to unmask this man by an old "friend" high in the Revolutionary government. Romance, betrayal, action and adventure, and wonderful characters had me not only reading this until I wore out two paper copies (so I broke down and bought an expensive hardcover library binding one!) but also had me collecting all sequels. I still don't have all of them but I do have most. Now, you can find all of them really on Project Gutenberg, etc.