Nigel searches the deserts and forests of Cretaceous Mongolia for Therizinosaurus, an obscure dinosaur with massive fossil claws, believing it to have been a huge carnivore. Throughout his journey, Marven comes face-to-face with dinosaurs such as Saurolophus, Protoceratops, Mononykus, Velociraptor and Tarbosaurus, a close relative of the famous Tyrannosaurus rex. Once Marven finds live Therizinosaurus he discovers them to have been a bizarre type of giant plant-eating theropod dinosaur.

In Middle Cretaceous Argentina, Marven searches for the largest dinosaurs of all time. He encounters a herd of Argentinosaurus, one of the largest sauropod dinosaurs, and observes the long and drawn-out hunt of the sauropods by one of the largest predatory dinosaurs, Giganotosaurus. During his journey, Marven also uses a small plane to fly with pterosaurs such as Pteranodon and Ornithocheirus, and he also encounters the massive crocodyliform Sarcosuchus.