The Scarlet Pimpernel by Baroness Orczy
I selected this book for First Son to read in seventh grade as his second "classic." It is one of the recommended books for Level 3 on the Mater Amabilis site. I assigned it as First Son's second classic, but I really think it was easier to read than Ivanhoe which he read earlier in the year.
The Scarlet Pimpernel is one of the first superhero books. The hero is a masked master of disguises, his identity a secret to all but a few trusted followers. The mystery of his identity is revealed before a grand escapade at the end of the book. It all wraps up rather nicely (and quickly) but it's a fun tale of adventure, courage, and heroism amidst the French Revolution.