John Buchan 
The Thirty-Nine Steps [EPUB ebook] 

Richard Hannay’s boredom with London society is soon relieved when the resourceful engineer from South Africa is caught up in a web of secret codes, spies, and murder on the eve of WWI. When a neighbor is killed in his flat, Richard, suspected, decodes the journal, runs to the wilds of his native Scotland in disguises and local dialects, evades Germans and officials…