The Isle of Glass (The Hound and the Falcon Trilogy)

Alfred, a healer with special powers, and Thea, a shapechanger, are captured when Crusaders capture the city of Constantinople

Alfred has settled down at last amongst his own people, as Lord Chancellor of Rhiyana. But old enemies will not let Alfred savor his new life, and he must prepare for the ultimate battle of wills against an evil whose power is even greater than his own.