The narrator (who is never named) returns from Hong Kong to visit a friend in San Francisco. His friend’s name is Mohun Dampier, a young man from an aristocratic family who likes to dabble in the occult.
The night is stormy when the narrator visits Dampier’s house, and he is surprised to find a note that tells him to not ring the doorbell but simply to come up the stairs. This annoys the narrator, but he understands why Dampier left the note when he sees him – Dampier has aged dramatically, and looks very unwell. Dampier makes a reference to his impending death, and the narrator is puzzled. Suddenly, a gentle tapping is heard behind the wall just behind the chair that the narrator is sitting in, as if someone is seeking entrance. Dampier stares at the wall with a strange look on his face, then explains to the narrator that there is no room behind the wall, even flinging open a nearby window for proof. No one is there.
Dampier asks his friend to remain, and explains that he has heard this tapping twice before, and explains the events leading up to this supernatural event.
Ten years ago, he lived in a lovely corner of San Francisco when he saw a beautiful girl with dark eyes entering the garden of the house next to him. The girl was so lovely and delicate that Dampier actually removed his hat as a mark of respect to her. Dampier tried to catch sight of the girl again, and even inquired about her background. Unfortunately, he learned that she was an orphan, the niece of the woman who owned the lodging house where he lived. She was poor, and if Dampier married her, he would lose his high social status. Additionally, he thought that getting to know the young woman better would destroy the perfection he had created in his mind. Besides, he decided that marriage might not be for him.
One day, Dampier learned that the young woman’s room was next to his own, with only a thin wall separating them. He knocked upon the wall one night, and was surprised when he was answered an hour later. Every night, he knocked on the wall and listened for the response, which was the only flirtation he would allow himself with the young woman of his dreams. Eventually, she ceased to knock back, and he assumed that she had come to hate him. He sought for her in the streets, but saw no sign of her. He angrily decided to forget her.
One night he heard a very faint tapping on the wall, but given his anger, he decided not to respond. The next morning, however, he learned from his landlady that the young woman who lived next to him in the lodging house had been sick for months, and had died the night before. With horror, Dampier realized that she used the last of her strength to knock against the wall, and he cruelly decided to ignore her.
Dampier raves about restless souls, and says that this is the third time he has heard supernatural knocking after her death. According to his occult studies, this means he will die. After the narrator leaves, he does die that very night.
Once more, the narrator is never named, and seems to serve mainly as a vehicle for the reader to hear Dampier's story. Bierce's stories are primarily driven by plot and imagery rather than characters, so he does not find it important to provide names for even so important a character as the narrator.
The title of the story is ambiguous. It may refer to the tapping coming from beyond the physical wall of Dampier's apartment as well as the ability of the young woman's spirit to contact Dampier beyond the wall of death.
This story presents another example of ghosts, which result when an individual dies in agony and leaves behind unfinished tasks. We never see the ghost of the young woman, but we do hear her tapping, which eventually results in the death of Dampier. This story has more of a romantic theme than others - it is Dampier's unrequited affection that causes the ghost of the young woman to plague him.
Knocking was a common form of haunting in the nineteenth century. For example, the Fox sisters founded the spiritualist movement in the United States in the mid-1800s on the basis of their claims that they could communicate with spirits who made their presence known through knocking sounds. Eventually, it was discovered that the Fox sisters were making these knocking noises themselves, and the movement was discredited.