Griff Rhys Jones continues his exploration of Britain's mountains with a journey across the Pennines, the natural barrier between Yorkshire and Lancashire. Griff ventures underground to the heart of the mountains in search of the source of one of the country's most important rivers. He also discovers how the workers of the Pennines fought to claim the mountains as their own as an escape from the industry of the cities, and meets the ramblers who proudly uphold the right to roam.