Ten-year-old James Harrison and his family have recently moved into East End Cottage, the last house on a lane in Ledsham. Before their arrival, workmen renovated the cottage's long-sealed attic into a bedroom for James. During the work, one of them dislodged a small bottle of greenish glass wedged behind the window frame. It broke on the floor and was swept away with the debris. After the men left, a strange gathering of air filled the room, compressing into small winds that rustled the rubbish and rattled the windows before subsiding.
James loves the cottage, with its creaking stairs, stone floors, and apple trees. His sister, Helen, prefers the modern houses on the nearby estate, and a squat mongrel called Tim has recently attached himself to the family. One afternoon, James finds that someone has written a list of archaic services on his mother's apple-selling blackboard outside the gate, including "Sorcerie," "Astrologie," and "Geomancie," a form of divination. Mrs Harrison assumes James is responsible. He suspects a boy from the village and visits Simon, a bespectacled boy from the same street, who denies it convincingly. The two become friends. That night, James finds clay models knocked from his shelf, and his eiderdown is twitched off the bed.
The disturbances intensify. Someone crosses out the doctor's instructions on Helen's cough prescription and substitutes an archaic herbal remedy in the same old-fashioned handwriting. The chemist refuses to fill it, and Mrs Harrison punishes James. While cleaning his room, he finds a message in his own red biro instructing him to help his father find a lost pipe by magical means and announcing that the writer and James will be very busy together. James also digs in the orchard and unearths a very old pair of wire spectacles. Later, another message appears on his mirror in his mother's lipstick: The writer claims the spectacles are his and warns James to serve him better than a former apprentice did.
James reasons through the evidence. No living person could be writing the messages unseen, Tim barks at empty air, and the writer knew about the spectacles before anyone else. He reluctantly concludes the presence is a ghost. He tells Simon, who is sympathetic but skeptical. They discover a notice tacked to the police station board advertising services in sorcery and the seeking out of witches, signed "Thos. Kempe Esq. Sorcerer," listing East End Cottage and naming James as his apprentice. James tears it down before anyone connects it to him. Simon suggests James try speaking directly to the ghost.
James attempts this while doing homework. Thomas Kempe has left a message insisting that Mrs Harrison's hayfever is caused by witchcraft. James tries to explain that modern society has penicillin and policemen, but the ghost responds with fury: Clay pots fly across the room, books hurl themselves at James's head, doors bang, and the bedcover leaps off the bed. James shouts that he will do whatever Thomas Kempe wants, and the room instantly subsides. Mr Harrison surveys the wreckage, and James takes the blame, losing pocket money and pudding.
James and Simon visit the library, where they read about poltergeists, spirits that manifest through noise and destruction rather than appearing visibly, and James recognizes Thomas Kempe's behavior. The ghost's meddling extends beyond the cottage. Mrs Verity, the elderly widow who lives across the road, reports that the doctor's surgery has been ransacked with no sign of forced entry. Thomas Kempe writes a message on the school blackboard accusing Mrs Verity of witchcraft and identifying James as his idle apprentice. Mr Hollings, the headmaster who teaches James's class, treats it as a joke and uses it for a history lesson. The ghost also leaves his name and the Harrisons' address at the vandalized surgery, bringing a policeman to the cottage. James raises the subject of poltergeists with his parents, but Mr Harrison dismisses ghosts categorically.
When the vicar visits, Thomas Kempe yanks a chair sideways under him and tips tea onto his trousers. James is blamed. Desperate, he asks Mrs Verity about exorcism, the practice of expelling spirits, and learns of Bert Ellison, a local builder who also handles hauntings. Bert, a large, practical man, listens without surprise and agrees to help. In James's room, Bert attempts to trap the ghost in a corked bottle surrounded by candles, but Thomas Kempe blows out all the candles. That evening, the ghost unleashes his worst rampage: Doors slam, the television breaks, and Tim is kicked by an invisible force. In his room afterward, James finds the bottle smashed, with a message warning the ghost will not be tricked "twyce." The word catches James's attention: It implies someone successfully exorcised Thomas Kempe before.
James investigates a mound of rubbish thrown out by the workmen and finds a leather-bound diary from 1856 kept by Miss Fanny Spence, a woman who once lived in East End Cottage. Aunt Fanny, as James comes to think of her, had invited her ten-year-old nephew, Arnold Luckett, for the summer holidays and had the sealed attic room opened for him. The diary records the same disturbances: broken china, archaic messages, and Aunt Fanny blaming Arnold, just as Mrs Harrison blames James. A first exorcism failed, but a second with a bottle succeeded: A pale blue flame entered the bottle, which was corked and plastered into the wall below the attic window. James realizes the workmen broke this very bottle, releasing Thomas Kempe for a second time.
James develops an imaginative friendship with Arnold across the years, conversing with him in his mind as they walk the same landscape a century apart. At school, Mr Hollings reads from an 1873 log book a mention of Miss Fanny Spence bringing coal and cakes to the schoolchildren, confirming her continued presence in Ledsham. Bert returns for a second exorcism attempt with a rowan stick and inscribed papers, but Mrs Verity's arrival interrupts the ritual, and the ghost vanishes.
Thomas Kempe's attacks escalate. He chalks an accusation of witchcraft across Mrs Verity's fence, writes threatening graffiti on the fire station and vicarage, and throws a brick through the chemist's window with a note naming James. The police return, but James is saved by an alibi from Mr Hollings. One evening, the ghost leaves a message in unusually small letters: He is weary of this town and does not understand the people's ways. That night, James wakes to discover Thomas Kempe has set fire to Mrs Verity's thatched roof. The family rouses the neighborhood and evacuates Mrs Verity. The fire brigade saves the cottage, but Mrs Verity goes to stay with her sister.
At the school's centenary exhibition, James feels a tightening of the air. Thomas Kempe pushes him toward a desk, where a message reads: "Helpe me to goe. Finde my resting-place, & putt there my pype & my spectacles" (222). James takes the pipe and spectacles and searches the churchyard but cannot find the ghost's grave among the worn and illegible stones. He finds Bert working inside the church. Bert reveals that while repairing flagstones, he broke through into a sealed vault and saw Thomas Kempe's name. James peers into the vault and reads the inscription on a solitary tomb: "HERE LYETH YE BODY OF THOMAS KEMPE APOTHECARIE HE DEPARTED THIS LIFE YE LAST OF OCTOBER AD 1629 IN THE 63 YEARE OF HIS AGE" (231). An apothecary was someone who made and sold medicines; the sorcerer could not have had his true title on a church tomb.
Bert places the pipe and spectacles on the stone. A pale blue light appears, slips down the walls, rests on the tomb, shrinks to a pinpoint, and vanishes. Bert tells James the ghost is gone: Thomas Kempe could never have adapted to the modern world. They reseal the vault, and Bert rides away on his bicycle. James walks home through the churchyard in the fading light, noticing bare autumn branches already holding tightly furled new leaves waiting for spring. He reflects on the continuity of time and feels content.