The Hound and the Falcon — Judith Tarr

Alfred of St. Ruan's Abbey is a monk and a scholar, a religious man whose vocation is beyond question. But Alfred is also, without a doubt, one of the fair folk, for though he is more than seventy years old by the Abbey's records, he seems to be only a youth.

But Alfred is drawn from the haven of his monastery into his dangerous currents of politics when an ambassador from the kingdom of Rhiyana to Richard Coeur de Leon is wounded and Alfred himself is sent to complete the mission. There he encounters the Hounds of God, who believe that the fair folk have no souls, and must be purged from the Church and from the world.