This three-part drama is based on real-life events that took place in an ordinary North London home in 1977. During the autumn of that year, novice paranormal researcher Maurice Grosse hears of a family reported to be terrorized by supernatural forces. After the recent death of his own daughter, Maurice gets drawn into the family's story, which also involves a young girl at the center of the bizarre happenings. The researcher enlists the help of experienced investigator Guy Lyon Playfair, who at first believes the case to be a scam -- that is, until he comes into contact with the malevolent presence.