This returning documentary following life at London Zoo has a new focus this series. They're hell bent on breeding critically endangered animals. This edition follows the journey of three Sumatran tiger cubs from the moment they are born to the last time they can be safely handled by keepers and vets, and revisits Flora the pygmy hippo as she continues to receive life-saving treatment for cancer. Plus, head of birds Adrian Walls and the team finally manage to breed their first-ever Humboldt penguin chick, which is soon joined by six more babies. Narrated by Sarah Lancashire.