Derren Brown, the mentalist known for exposing how people fool themselves, sets out to test the claims of Lou Gentile, an American ghost hunter with more than twenty years spent helping clients get rid of what they believe are unwanted spirits. Gentile does not just claim he can detect these presences; he argues some of them are capable of causing physical harm, and Brown follows him through several of his cases to see how that claim holds up. The film shows Gentile's methods in action, the equipment and techniques he uses to locate a haunting and then supposedly clear it, while people who hired him describe what drove them to call a ghost hunter in the first place: strange sounds, injuries, a sense of being watched in their own homes. Brown brings his mentalist's eye for how belief and perception get manipulated, pressing Gentile on whether his results prove anything or simply give frightened people a story that lets them feel safe again.