In 19th century Istanbul, the magistrate Kamil Pasha is assigned to find out who is stealing valuable relics throughout the city and selling them to London. He is instructed to find the relics and bring them back to where they belong. One of the relics is contained in a reliquary that has been guarded since the last days of the Byzantine Empire by a sect of Abyssinian descent called the Melisites. The relic is called the Proof of God.
Kamil is an upright and dedicated civil servant. While he is investigating, he learns about the history and beliefs of an odd group of people, the descendents of Abyssinian slaves who live in an abandoned cistern and are part of the city’s underworld.
In pursuit of the relic thieves and in investigation of some apparently related murders, we follow Kamil through the subterranean passages under Istanbul.
Kamil is also attracted to Elia, a refugee artist who lives in his sister’s house. Elia has suffered terribly, though, and is not really prepared to pursue more than friendship.
As with Barbara Nadel’s more modern Turkish mysteries, I find novels set in this exotic locale interesting, and the history presented in The Abyssinian Proof is fascinating. Sometimes, I wish that Kamil Pasha wasn’t quite such a serious man, however.
whatmeread 
I adore the cover and having just returned from a trip to Turkey, I want to return there — by books if I must! 😉
You might try the Barbara Nadel mysteries, too. Her books set in Istanbul usually involve one of the minority groups in the city. I think they’re pretty good.