Adventurer and naturalist Steve Backshall sets out to explore one of the wildest rivers in the world, the mighty Baliem River on the island of New Guinea. He’s on a mission to discover the ancient tribes that live along its banks, explore unknown caves and meet the dangerous animals lurking in the river and surrounding jungle. But the only way to discover these hidden worlds is to travel the river from source to sea—a feat that has never been achieved before. In this first episode, Steve starts his journey at Lake Habbema, the body of water where the Baliem River begins its life. Embarking on a perilous expedition, Steve encounters some of the most extreme whitewater rapids seen anywhere on the planet. Exploring the land alongside the river, Steve uncovers spectacular caves that have never been explored before. He also encounters some of the animals that are unique to this part of the island. Reaching the Baliem Grand Valley, Steve stays in a Dani village for the night, encountering members of this ancient tribe and sleeping next to the mummified remains of a 200-year-old Dani warrior.