This episode marks the beginning of Nigel's quest as he travels back to the Ordovician to find the giant orthocone. He then ventures to the Triassic to encounter Cymbospondylus but on his journey there, he encounters nothosaurs and the creature that defies physics. His last trek of the episode is to the Devonian where he encounters the Dunkleosteus.

This episode starts with Nigel still in the Devonian escaping the wrath of Dunkleosteus. The episode then moves on to the Eocene where Nigel encounters a rhino-like elephant and the giant Basilosaurus. The episode then continues to the Pliocene where he encounters the bizarre Odobenocetops and the titanic shark Megalodon.

This episode starts with Nigel still in the Pliocene still trying to attach a camera to a Megalodon. The episode then moves on to the Jurassic where Nigel comes face-to-face with the giant fish Leedsichthys, the marine croc Metriorhynchus and the giant monster Liopleurodon. The episode concludes in the Cretaceous, Hell's Aquarium. There, Nigel encounters a plethora of sea monsters and then come face-to-face with the deadliest sea monster of all.