Nigel goes back 75 million years to prehistoric Texas to try and rescue a Deinosuchus, the largest crocodile ever to have lived. On his arrival he encounters a couple of lost juvenile Parasaurolophus and narrowly escapes being eaten by two Albertosaurs, the top predators of their era.

Taking a tip from some airborne Pterosaurs, Nigel scouts the coastline in a micro-light aircraft and witnesses a massive Deinosuchus erupting from the water and catching one of the Pterosaurs. He then spots a Deinosuchus swimming inland up a creek and decides to follow it.

Back at Prehistoric Park, Suzanne the vet is bottle-feeding two saber-tooth cubs and worrying about the mammoth, Martha, who is isolated from the park's herd of modern elephants and not doing well. Meanwhile Bob is struggling to keep up with the demands of looking after so many prehistoric animals.

Back in prehistoric Texas, Nigel takes to a boat and has a near miss with a giant croc before finally making it to a freshwater lake where he finds both Deinosuchus and a herd of Parasaurolophus. After witnessing a kill, Nigel sets about building a Deinosuchus trap. He then heads back to the jeep to get the meat he needs to bait it, only to discover a group of carnivorous Troodon in the process of eating it. After scaring them away, he takes the remaining meat back to bait the trap only to have it stolen from under his nose by the persistent and intelligent Troodons.

Next morning, after witnessing an amazing battle between three Deinosuchus and a group of Albertosaurs, Nigel decides that with no bait left his only hope of catching a Deinosuchus is to lure it into the trap himself. His plan pays off and a giant croc chases Nigel out of the water and into the trap. When Nigel brings it back to the park, an unexpected stowaway causes a near disaster.