Faraday, a country doctor with humble beginnings, is called to Hundreds Hall, an 18th-century estate that has survived far beyond its former glory. He treats a young maid who dislikes the large, draughty emptiness of the house, but strikes a friendship with Caroline Ayres, the unmarried daughter of the family, her brother Roderick, who continues to heal physically and mentally from his experiences as a pilot in World War II, and their mother, the lady of the estate. He begins treating Roderick's lingering badly-healed wounds and becomes a family friend, knowing them well enough to realise they are in dire financial straits and unable to keep the house in any comfortable condition without selling their lands or objects in the house.
In an attempt to cheer up the family and possibly match Caroline to a potential husband, they throw a party for a few family friends when disaster strikes. A couple brings their young child who is mauled by Caroline's ancient and previously gentle Labrador retriever. Roderick begins to behave moodily and drink heavily. Faraday believes the strain of managing the estate is at fault. Roderick, however, divulges that something appeared in his room the night the dog attacked the girl. He says that it was first in his room trying to harm him, and that he must keep the unseen force focused on him so as not to direct its attention to his sister or mother. Spots begin appearing on his walls looking like burns, and, after Caroline awakes in the middle of the night to find his room on fire, Roderick is committed to a mental hospital.
Faraday and Caroline waver between romance and confused platonic friendship. Other sounds in the house alarm Caroline and Mrs Ayres and their two maids. They find curious childish writing on the walls where these activities have taken place. The maids' bells sound without anyone calling them; the phone rings in the middle of the night with no one on the line. A 19th century tube communication device linking the abandoned nursery to the kitchen begins to sound, scaring the maids. When Mrs Ayres goes to investigate, she is locked in the nursery where Susan, her much-loved first daughter, died of diphtheria at eight years old. Experiencing shadows and indiscernible fluttering and frantic to escape, Mrs Ayres pounds the windows open, cutting her arms. After Caroline and the maids free her and she recovers, she comes to believe and take comfort that Susan is around her at all times, that Susan is impatient to be with her though she sometimes harms her. One morning not long after, Caroline and the maid find that Mrs Ayres has hanged herself.
The day of Mrs Ayres's funeral, Faraday and Caroline set plans to marry in six weeks' time. Caroline, however, is listless and uninterested in the wedding, eventually calling it off and making plans to sell Hundreds Hall. Faraday is unable to believe it and tries several times to talk Caroline out of it, to no avail. On the night of their would-be wedding, Faraday has a call that keeps him out. When he finally comes home, he learns that Caroline hurled herself off the second floor onto a marble landing, killing herself. The maid reports at the inquest that she awoke to hear Caroline go upstairs to investigate a sound she heard in the darkened hall. She simply said "You!" then fell to her death. Three years later, Faraday continues to visit the abandoned mansion, unable to find what Caroline saw.
