Following his adventures foiling the plans of the Black Stone gang in The Thirty-Nine Steps, Richard Hannay is called in to investigate rumours of an uprising in the Muslim world, and undertakes a perilous journey through enemy territory to meet up with his friend Sandy Arbuthnot in Constantinople. Once there, he and his friends must thwart the Germans' plans to use religion to help them win the war, climaxing at the battle of Erzurum. As well as being a gripping adventure story, Greenmantle is surprisingly modern in the concept of using a Jihad to mobilise Muslim forces, and is disturbingly relevant to the modern world.

With an Afterword by Ned Halley.