Well, this is one of those old thrillers from the British Empire that is also set during World War I, and is a kind of propaganda piece about the greatness of the British, and the fallibility of the Boche (a pejorative term for German soldiers).
John Buchan wrote a series of adventures featuring Richard Hannay. Hannay was a mining engineer who made a pile in South Africa and finds living in idleness in England rather a bore. So, fortunately for him, he has adventures
. This is the second of the Hannay adventures.
The time is 1916 and the British are fighting back the Boche in Europe. Hannay is looking forward to going back into the fray, but is induced instead into helping with a spy mission. The spy agencies are certain that the Germans have plans to take over the Middle East, a place where the British have some interests, e.g. Egypt, Syria, Mesopotamia (Iraq).
So, Hannay is to be sent off to Constantinople to straighten things out. He's given a small team to help: an American, John S. Blenkiron, Ludovick Arbuthnot, who is known as Sandy, and another bloke, whose name I've forgotten (Peter?), but who knows how to get around in tight places. He can singlehandedly defeat hoards of marauding Bantus...or something. Sandy's expertise is in the Middle East. He can easily pass as a Turk, or Arab, or whatever is needed.
So, by various, improbably methods, sometimes pretending to be turncoats who are trying to join up with the Germans, they make their improbable journeys, each in his own separate way, to Constantinople to meet up. They find that the Turks, who are nominally German allies, can be manipulated by a "holy man", known as Greenmantle. It appears that Greenmantle is on his death bed, so that raises problems as well.
Well, I'll stop. What we have is lots of British posturing about their being a superior "race", superior even to the Germanic "race", lots of improbable, last-minute escapes from disaster, and so forth. Naturally, in the end it all comes out well for the good guys. Great literature, this is not. But for idling away a few hours with an amusing yarn, this isn't half bad.