From Britain's northernmost station at Thurso in Caithness, Michael Portillo heads for the ferry port of Scrabster to cross the Pentland Firth to the Orkney Islands. Passing the Old Man of Hoy, Michael takes in stunning views of the Orkney archipelago and the rugged coastlines of its 70 islands. Michael reaches land at Stromness on the largest of the islands, Mainland, and heads for Kirkwall, its most historic town. A visit to St Magnus Cathedral with a Norwegian historian sheds light on how much history the Orkneys share with Norway. Back in Stromness harbour, Michael joins a diving expedition to the former British naval base at Scapa Flow. It's one of the largest sheltered natural harbours in the world, well-placed for both the North Sea and the Atlantic. As divers explore the wreck of a dreadnought battleship, Michael hears how, in the aftermath of the First World War, nearly the entire German navy was scuttled here. Michael discovers defensive measures taken during the Second World War in massive causeways designed to seal the harbour's eastern entrances and learns about the beautiful, surprising legacy of the Italian prisoners of war who constructed them. From Mainland, Michael flies to North Ronaldsay, which lies further north than the southern tip of Norway and is known for its rare breed of coastal sheep. The youngest councillor on the Orkney Islands introduces Michael to her fellow islanders and their native, seaweed-eating sheep. Michael helps to patch up the 200-year-old sheep dyke, a Grade A listed drystone wall around 12 miles long. Back on Mainland, Michael admires the towering sea stack, Yesnaby Castle, located on the spectacular coastline, which inspired one of Britain's greatest 20th-century composers and conductors, Sir Peter Maxwell Davies. Michael learns about his prolific career from his partner, and on the cliffs at Yesnaby, listens to a string arrangement of his best-known work, Farewell to Stromness, played by schoolchildren from the island.