The last light of the sun - Guy Gavriel Kay

There is nothing soft or silken in the northlands, where for decades there has been bitter, bloody war between the Vikings, the Celts and the Anglo-Saxons. But times change, even in the north, and for a generation there has been peace... And yet, what has changed once can always change again…
Alun ab Owyn, grieving for his brother's death at the hands of the raiders, leaves his lands to become embroiled in the politics of the great. Bern Thorkellson, punished for his father's sins, commits an act of vengeance that brings him face-to-face, across the seas, with a past he's been trying to leave behind. And the shrewd King Aeldred shores up his defences with alliances and diplomacy - and with swords and arrows.
The death of a prince, the new life of an exile, and the dreams of a king will be the threads from which the tapestry is woven, and the world is changed forever...