The Book of the Stone — Diana L. Paxson

After years of conflict, Britannia finally knows peace and Artor reigns from his throne at Camalot. But discontent rumbles through the kingdom. A new generation longs for the glory their fathers knew. Medraut, the son conceived by deceit, lusts for Artor's crown -- and his queen. Dreams of an empire draw the king to Gallia to battle again, leaving the sovereignty of the isle in Guendivar's hands. As Artor's painful absence grows longer, the land cries out for its champion -- and even the queen doubts his return. With the rise of revolt home to a country in turmoil. Only he can heal the land and reclaim the kingdom -- or else the hallowed isle will be ripped asunder once again.

A darkness born and bred for revenge shadows the nation. But one hope shines -- the Defender of Britannia.