The episode starts with the crew erecting the prehistoric animal enclosures.Nigel immediately knows which animal he wants to bring back first: the huge and most famous dinosaur Tyrannosaurus rex. Nigel goes through the time portal, aiming to bring back a Tyrannosaurus rex. He finds a flock of Ornithomimus and tries to catch one by putting a sock over its head to quieten it, but must let it go when three Tyrannosaurus rex arrive. Nigel is pursued by the Tyrannosaurus rex, but they give up when he heads into the deeper forest where they cannot pursue as they are so top-heavy, tripping could kill them. He tracks the Tyrannosaurus rex to the middle of their territory. He finds some Tyrannosaurus rex eggs, hoping to bring some back for hatching, but they are broken and empty, either hatched or eaten.As he returns to camp, in the sky are meteors running ahead of the asteroid which will wipe out the dinosaurs. The next day he finds a herd of Triceratops. The pride of Tyrannosaurus rex attack the Triceratops herd. A female Tyrannosaurus rex is gored in the thigh during the attack. The male Tyrannosaurus rex back off, leaving the wounded Tyrannosaurus rex to catch her prey alone. It goes after a 3-ton young male Triceratops, Nigel opens the time portal and leads the Triceratops through it by waving his jacket at it matador-fashion. It follows him through but the Tyrannosaurus rex does not follow. The Triceratops is named Theo and becomes the park's first exhibit. Theo starts persistently charging the same tree, and his neck frill changes colour. Suzanne thinks that it is rutting. This gives Bob an idea. Nigel heads back through the time portal and finds a Tyrannosaurus rex track in volcanic ash, and sees by the dragged toes that it is the female with the gored thigh. Nigel sees that the Tyrannosaurus rex is walking alongside a river following a drifting Triceratops carcass. The carcass gets stuck in rocks in the riverbed. She cannot reach it and carries on downriver. Nigel and others build a crude stockade wall alongside the river out of local fallen timber, trying to funnel her through the time portal.A flock ofOrnithomimus appear and run ahead, and the Tyrannosaurus rex chases them through the time portal into the park. The Tyrannosaurus rex catches a straggler, a young Ornithomimus near Nigel and turns back. Instead of eating it there, she carries it towards the volcano despite her injured thigh. Nigel follows. Back at the park, Bob puts the Ornithomimus into their new paddock and gets back to his plan for Theo. Meanwhile, Nigel continues to follow the wounded Tyrannosaurus rex until he finds that she has two babies. Nigel plans to bring the Tyrannosaurus rex mother and her babies back to the park with him, but a male Tyrannosaurus rex attacks the female for her kill. In the ensuing battle, the male Tyrannosaurus rex smashes the female's head against a rock formation, an injury that results in the mother's death before her last roar to Nigel to save her children. At this point, a 6-mile-wide asteroid enters the Earth's atmosphere at 20,000 mph (32,000 km/h) and hits the Gulf of Mexico. The explosion is 7 billion times more powerful than the Hiroshima bomb, and its blast column can be seen in Montana. It leaves Nigel with three minutes while the blast front travels from Chicxulub to Montana at 200 times the speed of sound (c 245,000 km/h) and reaches him.Under a sky full of bright meteors, he uses the only meat that he has (what appears to be a ham sandwich) to entice the two young Tyrannosaurus rex through the time portal with a second to spare; a bit of the impact blast chases him through the Time Portal. In the park, they are put in an observation pen and named Terence and Matilda. The head keeper copes with Theo's rutting by making a "rival" for Theo by using old tires and oddments to build a crude mockTriceratops head and neck on the front of a tractor, providing something for Theo to take his aggression out on. Later, Terence and Matilda are moved to their new enclosure. The Park takes into account that keeping the pair under control is going to be a major challenge.