In 1921 England, we meet Florence Cathcart, a respected author known for her work on debunking supernatural frauds. Haunted by the loss of her lover during World War I, Florence teams up with the police to expose various claims of ghostly occurrences. Her latest case begins when she is approached by Robert Mallory, a teacher from a boarding school who seeks her help to investigate the mysterious death of a student named Walter Portman. The school has been buzzing with rumors of a child's ghost that appears linked to the boy's demise.
Upon arriving at the boarding school, Florence is driven by the hope of rationalizing the ghost sightings that have unsettled both students and faculty alike. Initially, these ghostly apparitions are dismissed as mere pranks conducted by the boys. However, as Florence delves deeper, she discovers that one of the teachers was the last person to see Walter alive and pressed him outside to "man up." This terrifying experience triggers an asthma attack in the child, contributing to his tragic fate.
The half-term break leaves Florence, Maud the housekeeper, and a lonely boy named Tom as the only inhabitants of the school. Tom reveals to Florence that his parents reside in India, making it difficult for him to return home. A perplexing incident occurs when an inexplicable hand reaches out for Florence from a nearby pond, causing her to faint and fall in, only to be saved by Robert. This event is misinterpreted by the other characters as a potential suicide attempt. Despite this, Florence pushes on with her quest to uncover the truth behind the ghostly mysteries.
As the investigation continues, Florence's bond with Robert grows, hinting at a burgeoning romance between the two. Simultaneously, a series of strange supernatural events unfold, leading to deeper revelations about the school's dark history. Edward Judd, the groundskeeper, who has a history of jealousy towards Robert, poses a dangerous threat to Florence in the woods. However, an unwitting confrontation leads to Edward's demise using the butt of his own gun, aided by invisible forces.
The narrative takes an unexpected turn as Tom's true identity is revealed—he is actually a ghost and Florence's half-brother, born to Maud. They grew up in the very home that is now a boarding school, where a disturbing family history has faded from Florence's memory. The ghosts of their pasts haunt them, and as Maud sees Tom, she confesses that he longs for family. In a tragic twist, Maud attempts to poison herself and Florence with the intent of reuniting in the afterlife. Nevertheless, Florence bravely refuses to succumb, vowing to be with Tom in spirit and not to leave him behind.
The conclusion leaves audiences wondering about Florence's ultimate fate. As she navigates her path, there is ambiguity surrounding whether she herself has become a ghost. Some interpretations suggest that only Robert can truly see her; other characters may perceive her only as a lingering memory. In the end, as Florence departs, she is approached by a child who can see Tom, emphasizing the theme of connection and unresolved pasts. The film concludes with a hopeful note, as Florence discusses her plans for a new book, suggesting that perhaps the antidote was successful, leaving the door open to multiple interpretations of her journey and existence.
