An unseasonal blizzard causes Paul and Carol Wilson, newly wed, to lose their way in the Ardnamurchan Peninsula in south-west of Scotland. They seek shelter for the night at an old dilapidated mansion and are brought into contact with a strange group of people engaged in a bizarre experiment.

Dominating everyone is Ardvreck House with its evil reputation, the scene of unsolved mysteries dating back to Victorian times. Trapped in the house by the worsening weather, the Wilsons and their hosts face terrfying and malevolent phenomena bringing them to the brink of sanity until they uncover the house's last secret, hidden for so long within its depths - the devil in the darkness.