Michael Portillo's coastal railway journey takes him past lochs and castles on the Far North Line to Britain's northernmost railway station at Thurso. From Lairg on the banks of Loch Shin, Michael heads for a secret conservation area in the 18-mile-long loch to track down one of Scotland's most elusive and endangered species, the freshwater pearl mussel. Michael wades into the water with an expert on the mollusc, who shows him how to spot their shells underwater through a glass-bottomed cone and explains why they are so highly prized. A glorious journey along the valley of the River Fleet delivers Michael to Dunrobin Castle station, which serves the castle, seat of the earls and dukes of Sutherland since the 13th century. Michael finds out about the second duke of Sutherland, who planned in the mid-19th century to clear his land of crofters in order to graze sheep. His name is forever associated with the misery and destruction of the Highland Clearances. At Brora, Michael hears how the Clearances affected the crofters evicted by the duke and learns about the purpose-built fishing villages to which they were sent. Two modern-day crofters show Michael how they are turning part of their coastal croft into a low-intensity farm. Back on the Far North Line, built by the third duke of Sutherland, Michael reaches Georgemas Junction, Caithness, where the local stone is a much-sought-after construction material. At Spittal Mains quarry, Michael learns to split a flagstone by hand with a heavy hammer.