Hannah Scarlett's cold case team are looking into the three-year-old mystery of the disappearance of Lily Elstone. Their investigation coincides with the disappearance of another teenage girl, Shona Whiteley, whose father Nigel lives in the Dungeon House, despite its tragic history - twenty years earlier, his uncle Malcolm Whiteley 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...