The Wizard in the Tree

Mallory notices there's something funny about an old oak tree, takes a closer look, and before she knows it, she's broken a magical spell. Arbican the wizard has been trapped in the oak for thousands of years, and his powers are gone. Will he get them back in time to save Mallory's village from greedy Squire Scrupner? 

Author: Lloyd Alexander

Publisher: Dell Yearling 

Released Date: 1981

ISBN: 0440495563