Unexplored - an unexplored region of the Peruvian Amazon is the start point for the search of Akakor. Rumours about an infamous river guide, Tatunca Nara are investigated.
Investigators head to Rio de Janeiro, where German journalist Karl Brugger was shot to death in broad daylight; in the jungle, a violent flood threatens to derail the search for Akakor.
Sandy Reed, the sister of missing explorer John Reed, joins in the search for her brother's remains; the team attempts a risky descent down a treacherous cliffside to find the entrance to one of the lost cities.
Deep in the Amazon jungle, the investigation tracks the final footsteps of the missing explorers; farther upriver, the team discovers a mysterious structure and its potential link to one of the lost cities.
The investigation uncovers a potential witness to the murder of one of the explorers; the testimony leads them to the scene of a grisly discovery that could break the mystery wide open.