Neil Oliver takes part in an aerial dogfight to discover why a Nazi flying ace landed his top secret new plane on Welsh tarmac at the height of the Second World War. Miranda Krestovnikoff visits a seabird paradise, the magical island of Skomer, and at Porth Oer, Alice Roberts attempts to solve the riddle of the "Singing Sands". What makes some very special British beaches whistle when you walk on them? Mark Horton visits and imposing castle at Harlech, one of the best preserved in Britain. Nick Crane explores the violent history of smuggling around the gorgeous Gower Peninsula and abseils into an extraordinary stone structure concealed in the side of a sea cliff.