Kwazii enters a shipwreck to get Calico Jack's map to an underwater city of gold. This leads the octonauts up the Amazon River, past parrots, freshwater stingrays, caiman and manatees. But a falling tree traps the GUP-A, and a tidal bore comes up the river, scattering the octonauts. Captain Barnacles looks for the others with the aid of a river dolphin and its echolocation abilities. The octonauts help an electric eel, a stranded arapaima, and get chased by piranhas. But a wood-eating panaque frees the trapped GUP-A. Meanwhile Kwazii has been saved by Calico Jack who turns out to be alive, but lost his ship after an attack by fire ants and an anaconda. His incomplete map had led him in circles, but Kwazii's piece completes it so they can finish the quest. After being blocked by hostile capybaras, they are reunited with the others in time to fight off more anacondas. Finally the "city of gold" turns out to be a colony of golden freshwater sponges in the bottom of a pool!

The Octonauts is a British children's television series, produced by Silvergate Media for the BBC channel Cbeebies. The series is animated in Ireland by Brown Bag Films but uses British voice actors. The TV series is based on American-Canadian children's books written by Vicki Wong and Michael C. Murphy of Meomi Design Inc