Greenmantle is a tale of intrigue and adventure set during the First World War. It features Richard Hannay, hero of the author's earlier novel The Thirty-Nine Steps. As he travels through Europe to foil a German plot and find an Islamic Messiah, he is joined by three more of Buchan's heroes: Peter Pienaar, a Boer scout; John Blenkiron, an American determined to fight the Kaiser; and Sandy Arbuthnot (Greenmantle), modeled on Lawrence of Arabia. The intrepid friends move in disguise through Germany to Constantinople to the Russian border to confront their enemies—the grotesque Stumm and the evil beauty Hilda von Einem.
I had just finished breakfast and was filling my pipe when I got Bullivant's telegram. It was at Furling, the big country house in Hampshire where I had come to convalesce after Loos, and Sandy, who was in the same case, was hunting for the marmalade. I flung him the flimsy with the blue strip pasted down on it, and he whistled. 'Hullo, Dick, you've got the battalion. Or maybe it's a staff billet. You'll be a blighted brass–hat, coming it heavy over the hard–working regimental officer. And to think of the language you've wasted on brass–hats in your time!' I sat and thought for a bit, for the name 'Bullivant' carried me back eighteen months to the hot summer before the war. I had not seen the man since, though I had read about him in the papers. For more than a year I had been a busy battalion officer, with no other thought than to hammer a lot of raw stuff into good soldiers. I had succeeded pretty well, and there was no prouder man on earth than Richard Hannay when he took his Lennox Highlanders over the parapets on that glorious and bloody 25th day of September. Loos was no picnic, and we had had some ugly bits of scrapping before that, but the worst bit of the campaign I had seen was a tea–party to the show I had been in with Bullivant before the war started. [Major Hannay's narrative of this affair has been published under the title of The Thirty–nine Steps.]