Dr. Hoo and the four children return to Zion Falls after defeating the troll army in the underground gathool kingdom only to find their beloved city under attack from their friends, family and neighbors. The citizens of Zion Falls are under the trolls' hypnotic control. The doctor and the young light bearers are the town's only hope. The threat lurking deep beneath the surface of the quarry lake is far more sinister than any foe they've faced so far. It is the Mooloom, the father of the gathool race. The final battle against the evil trolls is packed full of rip roaring action with sword fighting, tangling with a many-tentacled beast, and amazing underwater feats. Victory is achieved at a terrible cost. Now that the light bearers have triumphed releasing the townspeople from the thrall of the enemy, life in Zion Falls returns to normal. Update notes and gathool vocabulary are provided at the end. The final book in the "Troll Hunters" series promises hair raising moments and great battle sequences for young adventure seekers.