The episode is set in South America where the Amazon used to stand in 5 million years time. It features three species: (1) Carakiller, a descendant of the mountain caracara which has evolved to replace land predators; (2) Babookari, a descendant of the uakari which lives like baboons and has discovered how to catch fish; (3) Rattleback, a descendant of an agouti which has developed tough armour and can live through quickly-passing grass fires.

This episode shows that due to the cooling of the planet, the Amazon rainforest has vanished and has been replaced by grassland. Most primates have died out but the Babookari has evolved to live on the plains. They have also become much cleverer and can now make nets out of twigs to catch fish. There is also the rattleback, a heavily armoured rodent which is somewhat fireproof, and lives on a diet of Carakiller eggs, grass stems, and tubers. The episode also shows the biggest danger to these animals - fire.