John Buchan's classic novel, the second featuring the character of Richard Hannay. Preceded by Buchan's popular novel, "The Thirty-Nine Steps," Greenmantle tells the continuing story of Hannay. Set during the First World War, Hannay is called upon to investigate a German plot to foment trouble in Muslim nations to aid the German's war effort. Hannay travels to Constantinople (modern Istanbul), where he becomes embroiled in a plot culminating in the Erzurum Offensive (also known as the Battle of Erzurum), in which the Imperial Russian Army attacked Ottoman forces. Known for his works of fiction, John Buchan himself later rose to become the Governor General of Canada.