This episode starts months before the extinction of the dinosaurs. The last dinosaurs are depicted living under stress due to excessive volcanism. The episode focuses on a female 14 metre long Tyrannosaurus who abandons her nest, the eggs rendered infertile due to volcanic poisoning. Her calls for a mate are answered by a smaller male who has killed a young Triceratops and is eating it. Later, after repeated copulation, she eventually drives him off. The mother fasts for an extended period as she tends to her nest, dealing with raids by dromaeosaurs and marsupial Didelphodons. Only three eggs hatch and the mother brings down an hadrosaurid Anatotitan to feed herself and her brood. While defending her two surviving offspring several days later, the mother tyrannosaur is fatally injured by an Ankylosaurus. The chicks remain next to the carcass of their mother the next morning until they, and the rest of the non-avian dinosaurs, are killed when an asteroid slams into the Earth, a catastrophe that triggers the K-T extinction. A short final sequence shows the present-day Earth, dominated by large mammals, but still populated with numerous dinosaurs known as birds.