Chief Park Ranger Henry Shore has dealt with and fought real live dinosaurs at his beloved Crater Lake National Park for over six years. With the help of his rangers, a few brave FBI friends, and army soldiers, he'd been victorious over a prehistoric lake creature and years later some particularly fiendish, and clever, specimens of the flying variety. He and his newspaper publisher wife, Ann, thought their park was finally rid of the monsters and they could reclaim their tranquil life in a place they cherished. Not so.

For suddenly across the park new and even more malevolent mutant species of dinosaur begin to appear and create havoc, attacking the park's visitors and threatening its peace. And this time, the primeval scourge isn't confined to just their park. The creatures have moved into the nearby towns, across the western United States, and up into Canada. They are so much more aggressive, smarter, and hungrier than any that have come before and the infestation is spreading further and faster than Henry and Ann can even imagine. This time there's no easy way to defeat the dinosaurs. There's too many of them and they're too devious. This time it's full out war and the victor will someday claim Earth.