Deep in the heart of the Amazon, an uncharted lake emerges every dry season when the floodwaters recede. It's rumoured that this secret lair lures reptiles that have little changed since the time of the dinosaurs. Not just a few either; hundreds gather to this far off, inaccessible place. Outsiders come here at their peril; fishermen claim to have lost limbs to fearsome monsters. Are these exaggerated local legends? Or is the veil of mystery about to be lifted on one of the Earth's largest yet least studied carnivores the black caiman?