Mysterious Mr. Sabin

This thriller novel written by E. Phillips Oppenheim in 1898 revolves around Sabin, a ruthless French criminal mastermind, who plots the restoration of the French monarchy and the ascension of his niece Helene to the throne. To do so, he steals various military secrets as part of a complex plan involving a German invasion of Britain. He is foiled by Lord Wolfenden, a young Englishman who eventually marries Helene.