Shattered Oath, The (Prince of the Sidhe, 1)

Eirithan, ruler of Sidhe, is paranoid about threats to his throne, even when none exist. Swayed by political intriguers, he is convinced that his younger brother, Ardagh, is guilty of treason. His honor falsely destroyed, Ardagh suffers the worst of all possible fates—banishment to the land of humans. He is lost and alone in a world of Christian kings and Viking raiders.