Mike de Gruy and Kate Humble lead an international team of scientists and divers as they search for species new to science in the Amazon River. It is the climax of the diving expedition as the team explores a 90-metre chasm at the very bottom of the Amazon River. Scientists have no idea what lurks within. The team also explores overgrown jungle streams in search of giant caiman and electric eels - a fish that can stun you with a 600-volt shock. As the expedition draws to a close, the divers prepare to jump into the depths of the river to confront and film the extraordinary fish that lie in the abyss.