John Buchan 
Greenmantle [EPUB ebook] 

The second of John Buchan's five books with the Richard Hannay character is titled Greenmantle. London's Hodder & Stoughton published it for the first time in 1916. The other Hannay book set during the Great War is Mr. Standfast (1919). The Thirty-Nine Steps (1915), Hannay's earliest and best-known adventure, takes place in the years just before the war. Hannay travels through dangerous enemy territory to see his friend Sandy in Constantinople after being asked to look into reports of an insurrection in the Muslim world. Once there, he and his companions must foil German efforts to exploit religion as a weapon of victory, which will culminate in the battle of Erzurum. Hannay and his friend Sandy are in the book's opening scene recovering from injuries sustained during the Battle of Loos in November 1915. Senior intelligence officer Sir Walter Bullivant summons Hannay to the Foreign Office. Bullivant informs Hannay on the Middle Eastern political situation, implying that the Germans and their Turkish allies are planning to incite a Muslim rebellion that will destabilize the region as well as India and North Africa. Robert Baden-Powell and the Russian imperial family both read the book when it was first released as they awaited the outcome of the revolution in 1917.