Return of the Ice. The episode is set in North Europe, 5 million years into the future. The episode focuses on three hypothesized species: (1) Shagrat, a descendant of the marmot that has grown in size and developed thicker fur and a smaller nose to protect it from the cold; (2) Snowstalker, a descendant of the wolverine that has evolved sabre-teeth and white fur for camouflage; (3) Gannetwhale, a descendant of the gannet which has grown to immense size to replace the sea mammals. The episode explains that the onset of the ice age was very fast, so many animals died out. The ones that did survive had to have quick generations so they evolved fast. This is why rodents were successful. The episode follows the story of a female Snowstalker teaching her cubs to hunt, the Gannetwhale's breeding season and the mass migration to the south of the Shagrats.