The Crystal Sword

From the back cover of the Avon first edition: White magic - Dylan had always known the story of how his mother, Eleanor, had come from the far future, wielding the great Fire Sword, and how she had rescued England from the Plague of Darkness. Now the powers of Darkness again challenged the forces of Light - rekindling the primal battle and spreading it to distant lands beyond the shores of Albion. Only Dylan, Son of Magic, possessed the power to vanquish the evil and free the people from its thrall. But the noble prince was bewitched by a haunting beauty who had enslaved his dreams and lured him on a journey to the underworld... and an epic confrontation with the immortal Lords of the Caverns. The Crystal Sword - Where is it hidden? What is the secret of its lost powers? How can it save a menaced world?