When the death of his mother brings Nathan Appleby and his vivacious young wife Charlotte back to the family estate, they must turn the farm's fortunes around or risk ruin, and the devastation of the local community. Though the farm and its future demand their attention, when a vulnerable teenage girl is brought to Nathan, seemingly possessed by a terrifying spirit, he cannot leave her to suffer.

Nathan is a pioneering doctor who has worked at the forefront of the emerging science of psychology. He's an expert in mapping the dark places of the mind. Nathan believes there is always a rational or scientific explanation to be found for life's mysteries. So though Harriet's case is disturbing, Nathan must use every psychological technique he has to find a way to cure her. But what if Nathan is wrong - what if it's not an illness of the mind? Could Harriet actually be haunted?