This is the story of life on the razor's edge. A great mountain chain that spans the whole of the South American continent. In some places, they're an ice-world of massive glaciers. In other parts, a desert wasteland. And at its centre the largest rainforest on earth, where we meet some of the richest wildlife on the planet. Our journey through South America will include never before seem footage of piranhas, macaws giant river otters and the Andean bear the only species of bear found only in South America.