Wildlife adventure series following a team of explorers in the heart of the tropical island of Borneo - a lost world of unexplored jungle protected by a fortress of impenetrable mountains. Their aim is to find evidence that will help the area to be preserved forever. The team begin by setting up camp and searching for the elusive clouded leopard and the rare Borneo gibbon.

The humidity and parasites are starting to take their toll as one team begins searching for jungle elephants. Meanwhile, the mountaineers are lost on a remote mountain peak.

One team is hunting for bats, snakes and giant spiders, whilst the other finds extraordinary cave paintings made by an ancient rainforest people. Then the climbers set out on their greatest challenge yet - to drop into an enormous collapsed chamber lying at the top of a jungle mountain.

Steve and Justine are camped at the bottom of an enormous hole lying deep in the jungle. They are the first naturalists ever to explore this bizarre twilight world and they stumble across a network of caverns and passages, never explored by humans before. Meanwhile, Tara and her team face the white water rapids of a remote jungle river in order to be the first team of biologists ever to explore the pristine jungle that lies upstream.