The Golden Horn
by Judith Tarr
Book Two of The Hound and the Falcon.Constantinople, A.D. 1203: a great army camps outside the City of Cities, and threatens it with conquest. Within the City, a Greek witch and a renegade monk who is also a white enchanter do their utmost to hold back the tides of war. But even their great powers may not be able to save Byzantium's empire from the Western Crusade.