Dark Lord of Derkholm (Derkholm, 1) [Jones, Dianna Wynne]

Wizard Derk's world has been devastated for 40 years by Mr. Chesney's Pilgrim Parties--packaged excursions for tourists from the next universe. When Derk is chosen to play the Dark Lord this year, Chesney forces Derk to turn his estate in a labyrinthine castle and manifest himself into a nine-foot shadow. Can Derk find a way to put an end to Chesney and his parties?