The White Raven by Diana L. Paxson
One of legend's poignant love stories comes to life in this fantasy of betrayal set in the dark times of post-Arthurian Britain. Trouble begins when Morholt, a knight of the Celtic kingdom of Eriu, is killed in a duel. His death must be avenged, but will the Queen's sorcery destroy them all? Diana Paxon is the acclaimed author of many fantasy novels and short stories, including Westria Chronicles, Brisingamen and White Mare, Red Stallion.