"Greenmantle" by John Buchan is a novel published in 1916. Richard Hannay is drawn into a dangerous intelligence mission to investigate rumors of a German-orchestrated Muslim uprising during World War I. Traveling through enemy territory with trusted companions, Hannay must decode cryptic clues, assume false identities, and navigate a web of spies and conspirators. Their perilous journey leads to Constantinople and beyond, where they race to uncover the mystery of "Greenmantle" and prevent a plot that could change the course of the war. (This is an automatically generated summary.)