Greenmantle published in 1916.  It  started a new kind of genre: Spy Novels and International political thrillers. 
 
Richard Hannay, hero of The Thirty-Nine Steps, travels across war-torn Europe in search of a German plot and an Islamic Messiah. He is joined by three more of Buchan's heroes: Peter Pienaar, the old Boer Scout; John S. Blenkiron, the American determined to fight the Kaiser; and Sandy Arbuthnot, Greenmantle himself, modelled on Lawrence of Arabia.
 
The intrepid four move in disguise through Germany to Constantinople and the Russian border toface their enemies: the grotesque Stumm and the evil beauty of Hilda von Einem.