Because it was Poe's first tale of ratiocination, "The Murders in the Rue Morgue" introduces more basic features of detective fiction than any of Poe's other short stories. Among these basic features are three central ideas: (1) the murder occurs in a locked room from which there is no apparent egress. In later detective fiction, this idea is expanded (though essentially retained) and is used when the author sets the scene of the murder in a closed environment — that is, on a train, where the murderer is included among the passengers; on an island, where the murderer must logically still be there; or on an estate, where the murderer has to be among the people in the house. (In this particular story, with there being no way for the murderer to escape, the police are completely baffled.); (2) motive, access, and other surface evidence points to an innocent person. Frequently in detective fiction, the amateur detective is drawn into the case because a friend or acquaintance has been falsely accused, as is Le Bon (Adolphe de Bon), who "once rendered me a service for which I am not ungrateful." Thus, M. Dupin is drawn into the case because of an obligation to the accused; (3) the detective uses some sort of unexpected means to produce the solution. We have noted above that all of the clues should be present but, nevertheless, the appeal of detective fiction lies in the unexpected solution, which becomes logical only in retrospect.
Two aphorisms concerning detective fiction today are also presented for the first time in this story of Poe's. First, the truth is what remains after the impossible has been determined — no matter how improbable that truth may seem. That is, the police determine or surmise that there was no possible egress from the room of the murdered women. The door was locked from within, and all the windows were securely locked. Second, the more apparently difficult the case is and the more out of the ordinary the case is, the more easily, ironically, the case can be solved — by the key detective. For example, the problem in "The Murders in the Rue Morgue" that has the police so stumped is simply how can a nonrational, inhuman being break through the bounds of law, custom, and civilized order and commit such a gruesome and horrible atrocity on two well-protected women? The police cannot bring themselves to conclude that a "human" could possibly do this; the house is built in such a way as to protect it from the very acts which were committed there. The murders can only be solved, logically, when a person is able to place his human mind into conformity with a non-human mind and with the irrational acts of a beast.
