The Castle of Hape — Shirley Rousseau Murphy

Book 3 of The Children of Ynell series. As a child Ramad of the Wolves had sought the potent Runestone of Eresu that could save his world from the dark, only to have it shatter at the moment it came into his hands. Now as a man, leader of his fellow Seers in their war against the dark powers, he knows it is up to him to find and rejoin the shards before evil Seers can do so.A Kindle edition of this book is available in an omnibus titled The Runestone of Eresu,