Richard Hannay is tasked to investigate rumours of an uprising in the Muslim world and takes off on a hair-raising journey through German-occupied Europe to meet up with his old friend Sandy Arbuthnot in Constantinople, where they must thwart the Germans'' plans to use religion to help them win the war.  In Greenmantle John Buchan clearly asserts his mastery of the genre of the espionage thriller, by drawing on his wide first-hand knowledge of the worlds of politics and secret intelligence. Set during World War I, Greenmantle is a powerful meditation on the power of political Islam.