Sixteen-year-old twins Madeline and Catlin move to a new life in Ballyfrann, a strange isolated Irish town, a place where the earth is littered with small corpses and unspoken truths. A place where, for generations, teenage girls have gone missing in the surrounding mountains. As distance grows between the twins - as Catlin falls in love, and Madeline begins to understand her own nascent witchcraft - Madeline discovers that Ballyfrann is a place full of predators. And when Catlin falls into the gravest danger of all, Madeline must ask herself who she really is, and who she wants to be - or rather, who she might have to become to save her sister.