John Craven spends his last day of the series enjoying the breathtaking north Cornwall coast, while Jules Hudson is at home in Herefordshire discovering why a good dose of country air might not be all that it's cracked up to be. Two thirds of people in the UK are living with illegal levels of air pollution. Expert Mark Sutton from the Centre for Ecology and Hydrology reveals the best and worst places to live in the countryside. He also shows Jules how to identify lichen which can act as an early warning system. Margherita Taylor is in Northumberland at Hadrian's Wall, one of the latest national monuments to be besieged by illegal metal detectorists known as nighthawkers. Paul Martin is in the Brecon Beacons helping on a mission to save Britain's most endangered mammal, the water vole. Paul discovers how the voles' fortunes are being revived as he helps with a release back into the wild at Cosmeston Lakes in south Wales.