The Book of the Spear — Diana L. Paxson

Destiny lies in the clashing of magic steel. The hope of all Britain rests in the hands of the warrior sons.

A Saxon of royal blood, Oesc has fled the drowned, doomed country to which he is heir in order to claim rich lands in Britannia. Though sworn to the spirits of his new home, he truly serves an older god...and a darker sorcery: the power of the Spear. But the Spear's magic is opposed by that of the Sword of Rome, a weapon now wielded by young King Artor, and before him by Artor's father Uthir. In Uthir's hand, the blade slew Oesc's own father, and now vengeance burns fiercely in Oesc's heart--a lust for revenge that could destroy a greatness before it fully flowers.