John Buchan 
The Thirty Nine Steps [EPUB ebook] 

Richard Hannay arrives in London on the eve of World War I, where he meets an American agent seeking help in stopping a political assassination. Before long, Hannay finds himself in possession of a little black book that holds the key to the conspiracy — and on the run from both the police and members of a mysterious organization that will stop at nothing to keep their secrets hidden.
John Buchan’s
 The Thirty Nine Steps has been called the first great espionage novel. It has been embraced by each new generation and shows no sign of losing popularity.