Winter of the Ice Wizard by Mary Pope Osborne (audiobook)-110 pages in print
Teddy and Kathleen visit Jack and Annie in present day to deliver a message from Merlin. Jack and Annie's mission is to recover Merlin's staff from the Ice Wizard of Winter on the Winter Solstice, which actually turns out to be a message sent by the Ice Wizard to lure Jack and Annie to his palace to find his eye. They recover the Ice Wizard's eye from the Frost Giant who had been given the eye by the Fates. Teddy and Kathleen bring the Wizard's sister back to him and she forgives him, so Merlin and Morgan, who had been turned into white wolves by the Wizard, are humans again and the day is saved once again. I really enjoyed listening to these 4 Magic Tree House books on audiobook. I enjoyed reading them as a kid and they still bring some enjoyment, though not as much as back then.