David Attenborough seeks to understand why mammals are the planet's most successful creatures, visiting Australia and South America to study the lives of marsupials.

David learns why eating plants poses one of the greatest challenges to the planet's mammals. He takes a close look at a sloth who eats only leaves, and a rubble rabbit that turns poisons into preservatives.

A look at the dangers carnivores pose for other animals and the threats they face, from pack-hunting wolves, to arctic foxes, who store food for the winter, to big cats. Infared helps trail a lone leopard, and David searches for a Siberian tiger.

A look at omnivores, creatures that will eat whatever they can find, adapting to their situation and developing skills. Animals include bears that gorge on salmon before hibernating and raccoons with sensitive hands.

Attenborough explores the crystal clear waters of the Florida springs to swim with sea otters and dive with manatees.

David explores the vast range of tree dwellers mammals who have adapted to great heights. Featuring, the hyrax, tamandua, and flying squirrels.