Iolo Williams explores the Teifi, known as the queen of Welsh rivers. He heads upstream to the Teifi marshes and the old slate quarries near Cilgerran, where he finds a slow worm hunting in the open. He also meets Rod Bowen, a local coracleman, to learn about a 2,000-year-old fishing tradition. A major highlight occurs at Maes y Crugiau, where Iolo watches an otter as it hunts and eats an eel