The Tower and the Emerald - Moyra Caldecott - Bog

Viviane, a beautiful Celtic princess, unwittingly unravels the spell that binds the spirit of the evil Idoc within a circle of tall stones. Once released, the sorcerer-priest uses his powers to deliver vengeance upon those responsible for his original enslavement - including the Princess Viviane.
With Idoc in possession of the body of Prince Caradawc, her betrothed, Viviane can no longer judge safely between friend and foe, between this life and previous incarnations. Yet to rescue Caradawc from his nightmare, she must risk everything to reach the dreaded dark tower where Idoc waits. And, to ensure victory over evil, she must seek out Lucifer's Emerald.
She journeys through dreams and nightmare, beauty and horror, good and evil to save her lover and destroy the sorcerer-priest.
This is a quest for spiritual grace which is beautifully depicted and includes all the timeless ingredients of legend.