The Thirty Nine Steps - John Buchan, Vintage Classics

May 1914. Britain is on the eve of war with Germany. Richard Hannay is living a quiet life in London, but after a chance encounter with a mysterious stranger he stumbles into a hair-raising adventure - a desperate hunt across the country and against the clock, pursued by the police and a cunning, ruthless enemy. Hannay's life and the security of Britain are in grave peril, and everything rests on the solution to a baffling enigma: what are the thirty-nine steps?