Richard Hannay has been given as strange enigmatic mission that could change the outcome of teh First Wold War - he is to infiltrate the Muslim world and pursue the elusive 'Greenmantle'. His colleagues on the mission are the surprisingly subtle American John Blenkiron and Sandy Arbuthnot a young man with an excllent record with the Foreign Office.
Hannay himself is posing as Cornelis Brandt a Dutch South African with a grudge against England which is how he is able to get closer to understanding the only three clues e has been given to guide him on his way...