A killer is stalking Milly's preserve, but it's not the monstrous de-exinct Quinkanas—crocodilians the length of a bus. It's something far more lethal. Veterinarian Milly Smith cares deeply for each and every de-extinct animal living in the North American Pleistocene BioPark, a zoo and re-wilded wilderness sheltering resurrected megafauna, including mammoths, woolly rhinos, giant short-faced bears, and enormous apes. Her past is simple, and her present is rewarding. There's only one problem. Someone is trying to kill her. When a frenzy of Quinkanas is maliciously released into tunnels beneath the BioPark, she quickly realizes the people who released the animals are the same shadowy group who are hunting her. Milly is fiercely determined to save the Quinkana and bring the culprits who endangered the animals to justice. Barred from the rescue mission, Milly delves into the Quinkana lair alone, set on bringing the truth to light and keeping herself off the endangered list. Except … maybe luring Milly underground was their plan all along.