Writer and fisherman Will Millard tells the extraordinary story of how the River Taff came back from the dead. This river, once so polluted by heavy industry that no fish could live there, has now become one of the best salmon and trout rivers in Wales. Will travels from the source high in the stunning Brecon Beacons National Park to Merthyr Tydfil where he discovers that the town's ironworks were once vital to the British Empire. Along the way he trains with a mountain rescue team facing a unique set of challenges, meets a group of conservationists working to protect a magical, hidden valley and fishes for wild brown trout in the most unlikely location.