Twenty years ago, Malcolm Whiteley discovers his attractive wife Lysette is having an affair. The Whiteleys are wealthy, and live with their 16-year-old daughter Amber in the magnificent Dungeon House, overlooking Cumbria's remote western coast. But Malcolm is under financial and emotional pressure, and he begins to disintegrate psychologically, suspecting the men in their circle of being Lysette's lover. When Lysette tells Malcolm their marriage is over, he snaps, and takes out the old Winchester rifle he has been hiding from Lysette...

Back to the present day, and Hannah Scarlett's cold case team are looking into the three-year-old mystery of the disappearance of Lily Elstone, whose father was Malcolm Whiteley's accountant. Their investigation coincides with the disappearance of another teenage girl, Shona Whiteley, daughter of Malcolm's nephew Nigel. Nigel now lives in the Dungeon House, despite its tragic history. Twenty years earlier, Malcolm shot his wife and apparently killed his daughter before shooting himself. But as Hannah's team dig down into the past, doubts arise about what exactly happened at the Dungeon House twenty years ago...