The young heroes have escaped from the underground kingdom of the trolls, but a final battle still awaits them at Zion Falls, where the trolls are controlling the people's minds and using them to attack the children of the stars--will any of them survive?

Zak and the other young heroes must descend deep underground to face the creature that wears the lava crown and commands the troll army--can they rescue their mentor, Dr. Hoo and the captive humans, or has the doctor betrayed them?

Far above the small town of Zion Falls, the stars fall from the sky. Deep below the sleepy city, an ancient evil awakens. Caught in the middle are four teens with hidden powers beyond their wildest dreams.