The first-person narrator informs the reader that he is trying to recall and write down everything that happened to him earlier. He describes the Spanish Inquisition’s sentencing him to death, a sentence that he could not understand because of his extremely nervous state. When he regained consciousness temporarily, he felt himself being carried down and down into an apparent abyss. Later, when he was fully conscious, he knew that he was lying on his back in an oppressive, damp environment. Finally daring to open his eyes and finding himself in absolute darkness, he imagined that he was buried alive. Food and drink were provided to him only when he swooned or slept. Later, while investigating his surroundings, he narrowly escaped falling into a deep pit to a certain death. Shaken, but relieved, he fell asleep. When he awoke, some light entering the dungeon made it possible for him to compare the room to his calculations made in the dark.
Soon he discovered that one form of torture and execution had only been replaced with another, for he was strapped to a table so that only his head and left arm could be moved slightly. A large razor-sharp pendulum suspended overhead drew nearer with each pass. The ponderous rate at which it descended increased his agony, for he had to await death for what seemed to be many days. At last he developed a plan: He smeared some scraps of meat on his ropes so that the rats in the cell came to gnaw on them. Just as the pendulum brushed his skin, the ropes were loosened enough to allow him to escape. His relief was again short-lived, for the walls of his cell became hotter and hotter, forcing him toward the pit in the center of the room. When he resisted, his invisible tormentors moved the walls so that he was squeezed toward death by heat or by falling into the pit. At the moment when he was losing his foothold, the machines were suddenly turned off, and the walls receded. Just before he fell into the pit, he was rescued by General Lasalle, the leader of the French army, which had just invaded Toledo.