The Tae'anaryn and the Wizard's Apprentice

Kidnapped and tormented by an evil archmage who wants them to learn to harness the power of evil, Kialessa and Piex must find unexpected allies while they plan for their escape. It's not the wicked goblins that worry them, or the troll infested swamp, or even the towering rot dragon that keeps them there, but a simple riddle. Will they ever be able to return to their king and college again?