Featured Animals: Electric Eel, Black Piranha, White Blotched River Stingray, Redtail catfish, Marbled Swamp Eel, Common Trahira, Fidalgo.
Jeremy Wade returns to the Amazon to search for a mysterious and deadly killer with a reputation to match its awesome ability. Hearing the stories of three cowboys in Pará dying at the same time without any bite marks on them, he rules out piranhas and stingrays. After hearing a witness' claim, he concludes that the killer was an Electric Eel: an 8-foot, snake-like fish that possesses the bizarre ability to produce up to 600 volts of electricity. Following stories of "invisible powers", he journeys all over Brazil, searching for the elusive fish. Jeremy then comes across a story that confirms the eel's ability to kill a man, but he still tries to find out if it can kill three as the story claims. After searching through the smallest of ponds he can find in the dry season, he finally finds a large eel in little more than a mud-puddle. After fishing it out, Wade makes a startling discovery that could possibly explain three men dying at once.