This is the story of Florence Cathcart (Rebecca Hall), an author on supernatural hoaxes, who works with the police to catch charlatans and debunk supernatural phenomena. She is requested by Robert Mallory (Dominic West) to visit his school to look into the death of a student, Walter Portman, and find out if it has anything to do with the ghost sightings. Florence finds out that one of the teacher led the boy into an asthma attack by manning him up outside and scaring him. The school is then closed for half a term leaving only Robert, Maud (Imelda Staunton) the housekeeper and Tom, a lonely child, who tells Florence his parents live in India which takes too long for him to travel to.
Rest is how they solve the ghost sightings and the inexplicable noises, only to discover that the ghost was one of them.