The story begins with the narrator receiving a death sentence from the court of the Inquisition for an unknown crime. He describes the implacable horror of the judges as they announce their decrees, although the narrator himself is too overwhelmed with fear to understand their words and falls into a faint while longing for death. He awakens in darkness, wondering how much of what he remembers was a dream and how much was reality. At first, he swings between terror and confusion, but he then tries to remember the events of the past few days before opening his eyes. Realizing that he is unbound and in a dark dungeon, he reasons that he must not have been at an auto-da-fe, the typical manner of execution for those who ran afoul of the Inquisition. Instead of the public prayer and ceremonies that would have led to an auto-da-fe execution, he has been probably been placed in one of the dungeons of Toledo, a place known for particularly cruel tortures and punishments.
Fearful, the narrator again faints, and after he awakes for the second time, he begins to explore the dungeon while wondering what his fate will be. He discovers a stone wall and tears off a rag from his robe in order to mark a starting point so that he will know when he has circumnavigated the room. However, he trips, falls, and is overtaken by sleep before making a full circuit, and upon waking, he finds that someone has given him a loaf of bread and a pitcher of water. He finishes the circuit and, having counted his steps, he estimates the circumference of the cell to be about fifty yards, although he is unable to ascertain the shape of the prison. The narrator then decides to cross the center of the room, moving with increasing confidence until he fortuitously trips and lands prone at the edge of a circular pit. By dropping a stone from the masonry at the edge of the pit, he discovers that the pit is very deep and filled with water at the bottom. He hears a door closing and realizes that he has narrowly escaped his death.
The narrator's experience with the surprise of the pit is exactly in line with the horror stories he has heard of the Inquisition's punishments, and he decides that he would rather wait for death at the edge of the pit than risk the fall, deciding that the Inquisitors would not allow jumping into the pit to lead to an instantaneous death. Increasingly terrified, he remains awake for a long time but eventually falls asleep and wakes to again find bread and water by his side. However, the water is drugged, so he again falls asleep and wakes up to find himself in a slightly different situation. He can now see the cell by a sulfurous light and observes that the circumference of the room is only half what he estimated, since he must have nearly circumnavigated the dungeon before falling asleep and then accidentally backtracked the entire circuit after waking up. He also sees that the room is actually square, that the floor is made of the stone, and that the walls are made of large plates of metal and decorated with frightening figures. He can also see the circular pit in the center of the room.
The narrator observes his surroundings from the position to which he was moved while in his drugged sleep. He is securely bound on his back by a long strap that has been wound around his body and attaches him to a wooden framework so that he can only move his head and, to a lesser extent, his left arm, which he is able to use to take food from a nearby dish. However, he has not been provided with water, and the food has been heavily seasoned in order to produce the sensation of needing water. The ceiling, meanwhile, is thirty to forty feet above his head and plated with metal. One of the plates features a typical painting of the figure of Time, although Time appears to be holding an image of a pendulum rather than the more commonly associated scythe.
After a moment, the narrator notices that the pendulum is actually not an image and is in fact a pendulum sweeping slowly from side to side over a small trajectory. Confused, he observes it for several minutes but eventually turns his attention to the large rats that have been released into the dungeon. For some thirty or sixty minutes, he concentrates on scaring the rats away from his food, but when he again looks at the ceiling, he sees that the arc of the pendulum's swing is about a yard larger, that the pendulum is swinging faster, and that, most importantly, the pendulum has visually descended. The pendulum, he now sees, has a razor-like edge of steel and is attached to the ceiling by a brass rod. The narrator concludes to his horror that because he has managed to avoid their preferred form of punishment in the form of the surprise pit, his torturers have decided to find an alternative.
For an interminable period of time, the narrator watches the pendulum gradually swinging closer and closer to his body. At first, he prays for a swifter descent and, losing mental control, struggles to force himself closer to the blade, but then he suddenly calms down and smiles at the pendulum. Finally, he again faints; the narrator guesses that because the position of the pendulum had not noticeably changed, it must not have been an extended faint, but he also conjectures that had it been a long faint, his captors - who are clearly observing him closely - could have stopped the descent of the blade. He eats the remainder of the rat-plundered food and for a brief moment feels hopeful. On the edge of madness, he tries to hold on to the sensation of hope while observing that the blade was designed to cut horizontally across his heart. As the blade swings closer, he waits in a frenzied anguish for the blade to begin fraying his robes and vainly struggles to free his arm.
As his mental tension increases, he struggles between hope and despair, losing briefly to despair as he thinks about the tangled strap that restrains him. Nevertheless, he manages to pull his thoughts together for long enough to find a potential solution. He spreads the remains of the oil and spice from his food onto the strap and lies still so that the hungry rats swarm his body in order to eat away at the strap. By the time the rats free him from his bindings, the pendulum has already begun to slice at the robes above his chest, but he is able to break free away from the blade. As soon as he does, the pendulum is retracted to the top of the ceiling, proving to the narrator the closeness with which he is watched. He realizes quickly that something has changed in his prison and finds the source of the cell's light at a fissure at the base of the walls. An outside fire is heating his chamber, and the narrator rushes to the edge of the pit, weighing the cool water of the pit against the growing heat of the prison cell. He leaves the edge in a fit of tears.
The cell heats up further and begins to flatten into a narrowing diamond so that the narrator will eventually be forced into the pit. The narrator clings to the heated walls but is ultimately forced to the brink of the pit and screams in despair. As he is about to fall in, however, he hears voices and trumpets as the walls return suddenly to their normal shape. Having just led the French army into Toledo and beaten back the forces of the Inquisition, General Lasalle rushes in and catches the fainting narrator by the arm before he falls into the pit. The ordeal is over.
One notable aspect of Edgar Allan Poe's prose is his consistent use of detailed description, and he uses this tendency to great effect in his short story "The Pit and the Pendulum." The aim of the story is very simply to create a dark atmosphere of foreboding and anticipatory horror, and Poe achieves this by minutely tracking the path of the unnamed narrator's thoughts and experiences. Although the narrator is, like most of Poe's first-person protagonists, somewhat unreliable in nature, his unreliability is circumstantial, stemming from his fear and physical weakness rather than from guilt or inherent madness. However, because the narrator is very much aware of his unreliability and emphasizes it to us in a way that the narrator of "The Tell-Tale Heart" would not, he paradoxically gives us the sense that he is not trying to deceive. The sense of emotional honesty conveyed by the narrator leads to a sense of increased immediacy in the story and intensity of the mood.
Despite the lurid descriptions and the account of a relatively reliable narrator, Poe excludes certain details that heighten the suspense of the story. Just as he carefully tracks the psychological wanderings of the narrator, the author does not describe the wrongdoing of the narrator or the details of his arrest and later of his salvation. This omission of the facts has two major effects on the reader. First, it leads us to identify strongly with the narrator's confusion and fear of the unknown. One of the main sources of the protagonist's terror is that he either knows nothing about what will happen to him or knows the exact nature of his fate but cannot do anything with his knowledge. Poe exploits the theme of the fear of the unknown by connecting it to the fear of the dark at the beginning of the narrator's ordeal and to the fear of being helpless, as in the latter half of the story.
The second effect of our lack of information concerning the narrator's trial and sentencing is that we cannot ascertain his level of guilt or innocence. Part of the effect of the story is dependent on an assumption of the prisoner's relative innocence, particularly in the context of the cruelty of the Inquisition. The narrator's rescue from the Spanish Inquisitors by the French General Lasalle at the end of the story suggests that he may be a political victim driven to his doom as a result of worldly conflicts rather than sin, particularly since he was saved by the general himself rather than by a lesser soldier. In addition, the protagonist's oversensitivity and tendency towards introspection contribute to making him a sympathetic victim rather than a deserving prisoner.
Completing the atmosphere of terror in "The Pit and the Pendulum" is the use of nightmarish imagery. At the beginning of the tale, the narrator describes the "seven tall candles" that at first remind him of angels but then turn into "meaningless spectres, with heads of flame." We are reminded of a passage in the Book of Revelation, where seven candlesticks surround someone who resembles Jesus but who has flames in his eyes. Poe's Biblical allusion to the Apocalypse is related to the protagonist's constant sense of impending doom, as he is left with fewer and fewer choices other than death.
The most curious aspect of "The Pit and the Pendulum" - an aspect that sets this story apart from most of Poe's writings - is that the prisoner is abruptly and inexplicably saved from doom in the last paragraph, which is in line with the narrator's focus on hope. His punishment by the Inquisition is as much about mental torture as it is about physical discomfort, and accordingly, the narrator swings back and forth between hope and despair as well as sanity and insanity. Despite his frequent fainting fits, he is able to maintain enough of a grip on his mental facilities to survive the peril of the falling pendulum. However, by the time the walls begin to close in on him, he appears to be rapidly losing the battle for his sanity. Ultimately, his survival is not dependent on his own faculties, but it justifies the hope that characterizes his fight to stay alive throughout the ordeal.