In 1921, Florence Cathcart (Rebecca Hall) is a published author who works with the police to debunk supernatural hoaxes and thus to expose charlatans. It is revealed that she lost her lover in the war and that she "hunts" ghosts in an attempt to see if it is possible to bring him back. She receives a visit from Robert Mallory (Dominic West), a teacher from a boys' boarding school in Cumbria which had been a private home until twenty years earlier. Robert explains that there have been sightings of the ghost of a child at the school and that such a sighting might have been the cause of the recent death of a pupil. Although Florence initially refuses to help Robert investigate, his concern for the children - whom he describes as being almost like orphans - at the boarding school causes her to change her mind, since she is an orphan herself. At the school, she meets Maud (Imelda Staunton), the housekeeper, who tells Florence that she has read her books. After she conducts an investigation on her first night at the school, Florence comes to the conclusion that the sightings are the result of a prank, as two pupils had bullied a third into dressing as a ghost. With regards to the recent death, one of the teachers admits that he had forced the deceased pupil to stand outside the school in order to "man up" after he claimed to have seen the ghost, thus scaring the young boy and causing him to have a fatal asthma attack. The school then closes for half-term with the only occupants being Florence, Robert, Maud, and Tom (Isaac Hempstead-Wright), a pupil whose parents live in India.