"Would you enjoy living in a world lit by misty moonlight, a world where plants scream and vines try to grab you?" That's what Anthony Monday, his elderly friend Myra Eells (town librarian), and her brother Emerson discover is in store if the Autarchs—a group of hideously deformed sorcerers—have their nefarious way. It's up to the three intrepid adventurers to locate and destroy the crystal cube that's the source of the Autarchs' evil power. Throwing in plenty of conventional ingredients (ghosts, illusions, cryptic clues, secret passages, magic amulets, a witches' sabbath, cliffhangers, last-instant rescues, etc.), Bellairs dishes up a broth spiced with action, suspense, and his usual heap of lucky coincidences. More digestible than some of the author's recent offerings, with all three main characters taking active roles. (Fiction. 10-13)