The Eunuch of Stamboul

The Eunuch of Stamboul is a 1935 spy thriller novel by the British writer Dennis Wheatley. A British army officer is forced to resign his commission to avoid a diplomatic incident. He is dispatched to Istanbul and uncovers a plot to overthrow the government of Mustafa Kemal Atatürk and restore a traditionalist sultantate, led by a eunuch who serves as a senior secret policeman in the present government.

Film adaptation
The following year it was made into a film The Secret of Stamboul, directed by Andrew Marton and starring James Mason, Valerie Hobson and Kay Walsh.