The body of an 18-year-old TV personality Caitlin is found abandoned on a remote beach at the head of An Loch Dubh - the Black Loch - on the west coast of the Isle of Lewis. A swimmer and canoeist, it is inconceivable that she could have drowned. Fin Macleod left the island ten years earlier to escape its memories. When he learns that his married son Fionnlagh had been having a clandestine affair with the dead girl and is suspected of her murder, he and Marsaili return to try and clear his name. But nothing is as it seems, and the truth of the murder lies in a past that Fin would rather forget, and a tragedy at the cages of a salmon farm on East Loch Roag, where the tense climax of the story finds its resolution.