McCulley, Johnston: Zorro - The Curse of Capistrano
El Zorro, the Scarlet Pimpernel of California. This is the book that started it all. Written in 1919 (and out of copyright in the USA), this formed the basis for many movies and television series.
Who can ever forget Douglas Fairbanks, Jr. or Guy Williams as Zorro (or even Zorro, The Gay Blade with George Hamilton.) Riding through the night, making the sign of the "Z", when I was young every kid wanted to be Zorro.
The cover art is from the original serialization of the work and the book was published later.