Jack Tenrec must stop a rampaging dinosaur from destroying settlements. During the adventure, he meets Hannah Dundee, the Wassoon science ambassador who has just arrived at the City in the Sea.
An earthquake frightens a herd of Triceratops, who stampede toward an assortment of settlements. After an argument with Scharnhorst about how to handle the problem (she wants to kill them), Jack and his friends organize a Xenozoic cattle drive.
Jack and Hannah are hunted in the deep jungle by a cunning poacher, hired by Scharnhorst to prevent them from meddling with her plans to excavate an ancient train station and railroad line.
Jack, Hannah and Moustapha try to unravel the Loch Ness Monster-style mystery of a nocturnal creature who roams the streets of City in the Sea capturing its citizens.
Hannah's plan to house pteranodons in the City as a warning system against dangerous sea lizards is met with furious opposition from Scharnhorst and frank skepticism from Jack.
Using dynamite stolen from a deep-woods scavenger to frighten a pack of dinosaurs, the Terhune brothers inadvertently set off a huge blaze in the middle of the jungle which quickly spreads, approaching Scharnhorst's new gas wells.
