It is 1962, and Marta Khoury, a trailblazing marine archaeologist, has been called to Cairnroch, a small island off the east coast of Scotland. A Victorian shipwreck, dragged from arctic waters, holds the remains of a celebrated explorer and the treasures of his final expedition. But on her first dive down to the ship, Marta becomes convinced she has seen a dark figure lurking amid the wreckage.

When the Cuban Missile Crisis and the deep chill of a record-breaking winter keeps Marta stranded on Cairnroch, she forms a relationship with Elsie, a local woman working in the island’s only hotel. When the ship's artefacts inexplicably disappear, Marta and Elsie have to brave the freezing conditions to search for the missing objects before anyone else catches on. As something eerie seems to follow her at every step, Marta must confront if the haunting is a figment of her imagination, the repercussions from a terrible mistake from her past, or if something more sinister is at play that will trap her and everyone on the island—and their secrets—in an icy wilderness.