Chris Packham uncovers the secrets revealed by the DNA of Orkney's unique vole, Neil Oliver explores Orkney's tombs and monuments, Dr Shini Somara experiments to discover how the Orcadians could have moved giant blocks of stone over rough ground, and archaeological adventurer Andy Torbet climbs Orkney's most challenging sea-stack to unlock the story of Orkney's unusual geology.
Andy and some locals cross the Pentland Firth as the ancient Orcadians would have done.
Andy Torbet dives below the waves in search of the inspiration for the first stone circle.