In a condemned medieval London church, a demolition crew uncovers a walled up chamber with a skeleton inside. Black liquid crawls out of it and makes a haunted hose choke to death one of the workers. A skeptical police inspector is brought in but he deems the death an accident. However, a female journalist tries to convince him that there's more to the church than it seems. Meanwhile, a young man who feels a strange connection to the building tries to sneak in with his girlfriend. An old priest reveals that in medieval times the church was once used by a satanic cult led by a satanic priest until one of the cultists had a change of heart and betrayed the coven to the church which led to some of the cultists being caught and burned alive at the stake. Just before dying, they vowed revenge against both the traitor's descendants and the church itself.