Caught in a lightning storm, the Golden Condor crashes into the impenetrable forest of the Congo. There, our heroes are met by the guardians of this place, gorillas who escort them to the heart of their kingdom, next to a seemingly bottomless chasm. The Bako then guides Esteban, Zia and Tao to its home: Orunigi, the sixth city of gold, which to the children's great joy, opens to them. At the peak of this incredible tree-city, they find princess Rana'Ori who finally reveals to them the true goal of their mission: use the great heritage of Mu and Atlantis to prevent a great cataclysm which could destroy humanity!