An unnamed narrator opens the story by revealing that he has been sentenced to death during the time of the Inquisition—an institution of the Catholic government in fifteenth- and sixteenth-century Spain that persecuted all Protestants and heretical Catholics. Upon receiving his death sentence, the narrator swoons, losing consciousness. When he wakes, he’s in complete darkness. He is confused because he knows that the usual fate of Inquisition victims is a public auto-da-fé, or “act of faith”—an execution normally taking the form of burning at the stake. He is afraid that he has been locked in a tomb, but he gets up and walks a few paces. This mobility then leads him to surmise that he is not in a tomb, but perhaps in one of the dungeons. He decides to explore. Ripping off a piece of the hem from his robe, he places it against the wall so that he can count the number of steps required to walk the perimeter of the cell. However, he soon stumbles and collapses to the ground, where he falls asleep. 

Upon waking again, the narrator finds offerings of water and bread, which he eagerly consumes. He then resumes his exploration of the prison, determining it to be roughly one hundred paces around. He decides to walk across the room. As he crosses, though, the hem that he ripped earlier tangles around his feet and trips him. Hitting the floor, he realizes that, although most of his body has fallen on solid ground, his face dangles over an abyss. To his dismay, he concludes that in the center of the prison there exists a circular pit. To estimate its depth, the narrator breaks a stone off the wall of the pit and throws it in, timing its descent. The pit, he believes, is quite deep, with water at the bottom. Reflecting upon his proximity to the pit, the narrator explains its function as a punishment of surprise, infamously popular with the inquisitors. The narrator falls asleep again and wakes up to more water and bread. After drinking, he drifts off into asleep again, while imagining that the water must have been drugged. When he wakes the next time, he finds the prison dimly lit. He remarks that he has overestimated its size, most likely having retraced his steps during his explorations.