John Buchan 
The Thirty-nine Steps [EPUB ebook] 

London, May 1914. Europe is close to the First World War. Richard Hannay, a Scotsman raised in Rhodesia is living in London, and finds American Franklin Scudder at his door. Scudder is a photographer and free-lance spy and has information about a plot by the German spy ring, the Black Stone, to steal the British plans for war. Hannay later finds Scudder dead in his flat and decides he must carry on Scudder’s work. With both German spies and the police after, Hannay must solve the riddle of the thirty-nine steps alone.