"I don't like it, Arthur. Something's wrong here." The search for a stolen book plunges Arthur and Marya into another magical adventure as they are drawn into the web of the ghost of an Aztec witch with terrifying powers who has for centuries been protecting something deep underground. With the help of a skeptical Texas Ranger, the teenagers must unravel clues locked away in the towers of a creepy old mansion and uncover secrets shrouded in Aztec mythology, as they race to solve their most complex mystery ever. But it is only when they find themselves deep underground without the help of the Ranger that they realize that there is far more to the mystery than they ever imagined; they have been drawn into an ancient conflict and have become the target of evil forces they could never have thought possible.