The Green Pearl and Madouc(1983)

Jack Vance

In Lyonesse: The Green Pearl and Madouc the magical lands of high enchantment - the Elder Isles, the land, long-vanished beneath the ocean, from which King Arthur's ancestors fled to Britain - come to brilliant life again. In this ancient land the realm of chivalry and the world of faerie exist side by side and it is a place of strange beauty, high adventure and eerie magic. Warring kings renew their conflicts, opposing magicians devise ever more strange and sinister stratagems and Madouc, ostensibly the daughter of the ill-fated Princess Suldrun but in reality a changeling, becomes embroiled in political rivalries, military adventures - and the quest for the Grail.