Abyssinian Proof, by Jenny White

This is the second Kamil Pasha mystery, after The Sultan's Seal (2006).  The books take place in Istanbul during the late 19th century.  Kamil is a magistrate and a Pasha, a bachelor and a bit of a ladies' man.  In this book, Kamil is charged with stopping the thefts of religious artifacts, which are causing increasing friction among the religious groups living in Istanbul.  He has a personal interest in these thefts through his friendship with Malik, who holds the position of caretaker of The Proof of God within a secret sect of Melisites.  The supporting cast might be a bit overdrawn:  Omar the policeman, Avi the waif, Gudit the very creepy midwife, Balkis the priestess, Saba the priestess to be, and Elif, the artist/love interest.  Reviews say White did a huge amount of research about the place and time. 

Nadia May is a great reader.