The Freeing - Book and Key, #2

Sixth grader Thomas Gaines is sick all the time. But when he receives a magical book, with a key on a woven cord that he can wear as a pendant, Thomas is transported to a different world where he is healthy and strong. The world is the kingdom of Uwd-pronounced "ood, " like something an owl would say-and it's ruled by a good king named Adon who gives Thomas an important mission. A large, gray dog accompanies Thomas through many dangers, and with guidance from his magical book and his faithful companion, Thomas finds that his key has a particular purpose for his mission.
And whether or not he can overcome his enemies will matter not only in Uwd, but on Earth as well.