Sydney has been under siege by giant carnivorous animals from the outback for thirty years. In a 1950s-era Australia, Bruce Buckley believes a stone his uncle had taken from Ayers Rock was responsible for unleashing vast magical changes in the wildlife causing most of the country to be overrun. Sydney was only saved due to its new animal allies: boxing kangaroos, diprotodon-sized wombats, friendly koalas, secretive platypuses and laughing kookaburras. Bruce journeys between the various animal groups as they try to work out the cause for the current crisis.
Travelling around Sydney, he explores this city which has undergone many changes since the old days: kangaroos hop along the streets, where they are ridden by humans--the main method of transportation now. These kangaroos hold crowded boxing matches at the SCG, the brutality of which Bruce witnesses personally.
Many humans head out on expeditions into the dangerous lands outside the city, and Bruce crosses paths with one of the worst of these rough characters: Outback Jack, organising his own quest to find some lost opals. While doing so, Jack has his own problems with an atrociously biased kangaroo court and other leaders.
Koalas are now a part of human society, holding important positions, and living throughout the city as the two species work together to try and stay safe from outback foes. Meanwhile wombats have taken over Sydney's underground stations and constructed many other burrows, holding duels to settle disputes, and struggling to fight off underground enemies.
Kookaburras nest along the Harbour Bridge, busy conducting aerial patrols against enemy snakes and birds of prey. Platypus live secretly underwater, and are difficult to contact. Sydney's beaches are now heavily guarded against attacks from giant creatures of the ocean.
With some distrust and different motivations, Bruce and Jack join forces, visiting the different animal groups, while trying to find out more about the magic surrounding the stone from Ayers Rock.