John Buchan 
Greenmantle [EPUB ebook] 

Hannay is summoned to the Foreign Office by Sir Walter Bullivant, a senior intelligence man, whom Hannay met and assisted in The 39 Steps. Bullivant gives Hannay an outline of the political situation in the Middle East, and hints that the Germans and their Turkish allies are plotting to cause a great uprising throughout the Muslim world, that will throw the whole of the Middle East, India and North Africa into turmoil; Bullivant proposes that Hannay takes on the task of investigating rumours.