Holly Morris rides a cargo boat 250 miles down the Peruvian Amazon, three days packed onto a deck with more than 200 locals, hammocks, and cargo, bound for Iquitos, the largest city in the region and one with no road access anywhere in the world. She traces how Iquitos boomed a century ago on the rubber trade and meets members of an indigenous community whose ancestors worked as rubber tappers, hearing what that history cost them. The journey shifts register at the end, moving onto a restored historic steamboat for a run through the Pacaya-Samiria National Reserve, where the film lingers on wildlife along the riverbanks, including the rare pink river dolphin. Throughout, the focus stays on the boats themselves and the people who depend on them, cargo handlers, traders, and passengers for whom the river is the only road. It is one episode of a series built around punishing boat journeys in extreme environments, this one an immersive look at how the Amazon still runs on its waterways.