When Mary (Kate Dickie) and her teenage son, Fergal (Niall Bruton), move to yet another new home, it soon becomes clear they live their lives on the run, hiding from someone or something, terrified of being found. Trying to make new friends or connections wherever they go, Fergal finds himself caught between the affections of his beautiful and feisty neighbour Petronella (Hanna Stanbridge), and his fiercely protective mother, who will stop at nothing to protect her precious son.

Mary has strict rules that govern Fergal's life without which chaos and terror threaten to ensue. Their hunter is Cathal (James Nesbitt), a dangerous and terrifying man, intent on tracking down and killing Mary and Fergal. What's more, he is using a dark form of magic to find them. Mary's only defence is to use the same ancient form of magic in order to protect her son.

But how long will it be before Cathal manages to outsmart her? When local residents begin to be brutally murdered by an unknown life force, the sense of fear escalates. Is Cathal the beast responsible for the killings? Or is it the beast that he is trying to destroy?