The narrator explains at length his theory on "The Imp of the Perverse", which he believes causes people to commit acts against their self-interest. This essay-like discussion is presented objectively, though the narrator admits that he is "one of the many uncounted victims of the Imp of the Perverse". He then explains how his conviction for murder was the result of this.
The narrator murders a man using a candle that emits a poisonous vapor. The victim enjoyed reading in bed at night and, using the candle for illumination, dies in his poorly ventilated room. No evidence is left behind, causing the coroner to believe the man's death is an act of God. The narrator inherits the man's estate and, knowing he can never be caught, enjoys the benefits of his murderous act for many years.
The narrator remains unsuspected, though he occasionally reassures himself by repeating under his breath, "I am safe". One day, he notes that he will remain safe only if he is not foolish enough to openly confess. In saying so, however, he begins to question if he is capable of confessing. He fearfully runs through the streets, arousing suspicion. When finally stopped, he feels struck by some "invisible fiend". He reveals his secret with "distinct enunciation", though in such a hurry as if afraid of being interrupted. He is quickly tried and convicted of murder and sentenced to death by hanging.