Scotland, 1803. A rejected marriage proposal compels a doctor to escape to the Highlands, where he takes care of a local family. What started being as a rural retirement soon becomes a dangerous challenge when he realises that the inhabitants of the house are more threatening than the wild mountains themselves. In the cruellest point of the winter, a mysterious illness descends on the house, turning people into monsters. The servants claim that a bhampair is hiding among them, but Mrs McLean doesn't give credit to the their pagan beliefs and tries to find a logical explanation. The doctor wants to develop a vaccine against the disease, but he is hunted by the memories of his bloody past. Who is the real monster inside the isolated mansion in Glenfinnan?