Plot: 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