On Eriskay, Nick Crane explores the unique nature of the island's close-knit communities, and on the Isle of Lewis he meets the leader of the 'guga hunters', a small band of men following the age-old tradition of catching guga, young gannets which perch precariously on the sea cliffs of a remote and rugged lump of rock far out in the wild Atlantic. Neil Oliver explores the tragic shipwreck of the Iolaire. On New Year's Eve 1918, over 200 servicemen returning home from the First World War drowned within sight of their homes on the Isle of Lewis as the Iolaire was torn apart in ferocious seas. The disaster is little known outside the Western Isles, but the community of Lewis still grieve in private nearly 100 years later. Neil seeks out the last witness, who shares her first-hand memories of the Iolaire tragedy, giving a unique personal insight into this rarely-told tale. Miranda Krestovnikoff travels north to Shetland to search for the shy otters which struggle to survive on this wild coast. Tessa Dunlop is on a deep-sea survey ship to see how the epic voyage of HMS Challenger, the greatest scientific expedition of the 19th century, first revealed the astonishing secrets of life in the depths of the world's oceans, a global quest that began with surprising discoveries of mysterious creatures deep in Scottish seas in the 1860s.