Seven miles off the coast of Scotland and cut off by the tumultuous Pentland Firth, the fastest-flowing tidal race in Europe, Orkney is often viewed as being remote. However it is one of the treasure troves of archaeology in Britain, and recent discoveries there are turning the Stone Age map of Britain upside down. Recent finds suggest an extraordinary theory — that rather than an outpost at the edge of the world, Orkney was the cultural capital of our ancient world and the origin of the stone circle cult which culminated in Stonehenge. In the third of this three-part series, Neil Oliver, Chris Packham, Andy Torbet and Dr Shini Somara join hundreds of archaeologists from around the world who have gathered there to investigate at one of Europe's biggest digs. Andy dives below the waves in search of the inspiration for the first stone circle, Chris and Neil spend the night on an abandoned island as they hunt for clues as to why cultures change, Shini tests the technology behind a Bronze-Age sauna, and the archaeologists uncover a remarkable find.