In 1977, in London, Peggy Hodgson has financial difficulties to raise her children Margaret, Janet, Johnny and Billy since her husband has left her to live with a neighbor. When her daughter Janet sleepwalks and claims to talk to the spirit of an old man, Peggy does not believe in the beginning. But soon she witnesses supernatural phenomena in the house and concludes that Janet is possessed by a demon. Her neighbor and friends call the police and the officers also see the mysterious event. One of them tells the local priest and Ed Warren and his wife Lorraine Warren are invited to travel to London by the church to team up with the paranormal investigators Maurice Grosse and the skeptical Anita Gregory to see whether it would be a hoax. They witness weird events but they do not conclude it is true. What is happening in the Hodgson house?