A number of years ago, a friend in Istanbul mentioned several times that many of his friends and acquaintances in classical music, cinephile, and other high culture circles in the Turkish capital were crypto-Jews. I had no idea what he was talking about until I did some research into the Donme (or Donmeh or other variant spellings), and discovered that they were the descendants of followers of the Jewish False Messiah of the 1660s, Sabbatai Zevi (spellings vary), who after Zevi's apostasy, had publicly converted to Islam but had continued to worship Zevi, and remained a small, relatively endogamous elite who played key roles in Turkish revolutions and subsequent life.
For example, the foreign minister in Turkey's most recent Kemalist party government, Ismail Cem, was a Donmeh. (Perhaps a certain amount of the former neocon ardor for Turkey as the Good Muslim Country, which was so rudely interrupted in early 2003 when the Turkish parliament voted to not allow the U.S. to use its big base in Turkey to invade Iraq, much to the surprise and dismay of Paul Wolfowitz, had to do with Americans and Israelis being used to dealing with Turkish diplomats with many of whom they felt culturally compatible.)
The Donme are fascinating in an Umberto Eco sort of way, so, back in 2006, I wrote four long blog posts about them. The Donmeh are representative of how in the realm of the old Byzantine Empire, things are lot more, well, byzantine than we poor dumb Americans assume. We think of Muslim lands as uniformly Islamic, but there are millions of people there who are only vaguely Muslim, like the tens of millions of Alevis in rural Turkey and the ruling Alawi minority in Syria, not to mention the 50,000 Gnostics in Southern Iraq who believe in "planetary archons," and the Lucifer-worshiping Yezidis in Kurdistan. Then there are the Samaritans of Israel and the Druze, who won't tell you what they believe. There are people in the Middle East who worship a sword stuck into the ground and others who worship a large black dog. If it sometimes seems as if the U.S. government doesn't have much of a clue what we are dealing with over there, well, one reason is that it doesn't.
Kirsch's review confirms the history of the Donmeh I reported, but when he gets to recent generations after Kemal's revolution, he more or less announces, "Nothing to see here, folks, just move along, nothing to see. This topic is much more boring than it sounds. It's purely of antiquarian interest."