Whereas in
THE PURLOINED LETTER Poe gave his readers a definite crime, followed by a lot of windy philosophizing, before revealing the crime's solution.
In THE IMP OF THE PERVERSE, though, Poe spends half the story having a monologist explain his theory that the human possesses a hitherto unacknowledged "principle of human action," which he calls "perverseness," which exists to make the subject act against his best interests.
The phrenological combativeness has for its essence, the necessity of self-defence. It is our safeguard against injury. Its principle regards our well-being; and thus the desire to be well, is excited simultaneously with its development. It follows, that the desire to be well must be excited simultaneously with any principle which shall be merely a modification of combativeness, but in the case of that something which I term perverseness, the desire to be well is not only not aroused, but a strongly antagonistical sentiment exists.
The monologist gives three examples in which the principle of perverseness interferes with the subject's self-preserving actions: a speaker's tendency to talk around his subject, thus irritating his listener; general procrastination about needed tasks; and finally, a tendency to want to throw oneself into an abyss no matter how aware one is of the physical threat-- which might be used as Poe's justification for writing about horrific subject matter:
And this fall—this rushing annihilation—for the very reason that it involves that one most ghastly and loathsome of all the most ghastly and loathsome images of death and suffering which have ever presented themselves to our imagination—for this very cause do we now the most vividly desire it. And because our reason violently deters us from the brink, therefore, do we the more impetuously approach it. There is no passion in nature so demoniacally impatient, as that of him, who shuddering upon the edge of a precipice, thus meditates a plunge. To indulge for a moment, in any attempt at thought, is to be inevitably lost; for reflection but urges us to forbear, and therefore it is, I say, that we cannot. If there be no friendly arm to check us, or if we fail in a sudden effort to prostrate ourselves backward from the abyss, we plunge, and are destroyed.
Finally, after all these ruminations-- strangely dependent on the supposed revelations of phrenology-- Poe finally has his monologist reveal that he is the best example of perverseness, because perverseness has placed in him in prison, waiting for the hangman. In order to secure an inheritance, the monologist used a poisoned candle to kill his intended victim. The crime went undetected for some time, until at least the speaker could no longer stand holding the secret, and revealed all to the authorities-- not out of guilt, but just for the perverse pleasure of plunging into the abyss.
The murder is certainly a bizarre crime by any reckoning. And though the narrator is not a "psycho" in the usual sense of the word, he does commit one psychologically unstable act, even though only he is harmed by it.
