The movie is set in 1921 England where Florence Cathcart (Rebecca Hall) is a published author on supernatural hoaxes who works with the police to expose charlatans and debunk supernatural phenomenon, having begun her foray into her profession upon the death of her lover in (World War I) Upon a visit from Robert Malory (Dominic West), a teacher from a boarding school with the request to investigate the recent death of a student and how it is related to sightings of a ghost of a child, she travels to the school hoping to explain the sightings and the death. However, everything she believes in is put to the test as she begins to experience things that lie beyond the realm of science.

1921 England is overwhelmed by the loss and grief of World War I. Hoax exposer Florence Cathcart visits a boarding school to explain sightings of a child ghost. Everything she knew in unravels as the missing begin to show themselves.