Detective fiction is a curiously self-referential genre. Other genres may discuss themselves, for all I know, but this does seem to be a very common theme in detective stories. Sherlock Holmes talked about C. Auguste Dupin, Dorothy L. Sayers talked about the plot to one of the Father Brown stories in Busman’s Honeymoon, and both Agatha Christie and Sayers introduced successful female mystery writers as important characters into their stories. Moreover, more than one popular mystery writer wrote a list of rules for detective fiction, and The Detection Club had this initiation oath:
Do you promise that your detectives shall well and truly detect the crimes presented to them using those wits which it may please you to bestow upon them and not placing reliance on nor making use of Divine Revelation, Feminine Intuition, Mumbo Jumbo, Jiggery-Pokery, Coincidence, or Act of God?
It makes sense that a genre so thoroughly about analyzing people and situations should consider itself; indeed it does this both of curiosity and necessity. The necessity arises from the sort of game which is typical of mysteries, where the author “wins” if the reader does not guess the villain, but does blame himself and not the author once the detective’s reasoning is revealed. Once a trick has been used, readers are on the lookout for it and will probably spot it again. Conversely, because they are on the lookout for it, that expectation can be used to hoodwink the reader. Since both authors and readers play this game, both must analyze the stories written so far.
Especially in their early days, detective fiction did not garner a great deal of respect, even sometimes from its authors. Sir Arthur Conan Doyle actually killed his detective off in order get more time to write historical novels, and SS Van Dine lamented once his real name was revealed that he would never be taken seriously again. Charges that murder mysteries are unserious literature, or make sport of death, or a host of other complaints about, though people who love mysteries abound more.
A Franciscan brother who is a philosophy professor and fan of murder mysteries (and spy thrillers) told me the following theory: in a murder, intelligence has been used for a wrong end, damaging the natural order of things. He benefited unjustly from his crime, and since no man is an Island, all of society shares in this unjust benefit. (It also shares in the unjust harm of losing the victim, but that can’t be repaired.) The detective, through a right use of reason, untangles the web which was tangled by the murderer, and restores the right order of things. Once the murderer is brought to justice, the unjust benefit is removed and neither the murderer nor society by extension enjoys unjust benefit any longer. Murder mysteries are, therefore, symbolic of our redemption from sin.
I rather like this theory as it explains several things. First, it explains why it is acceptable when the detective catches the murderer but lets him escape when the murderer was doing no more than justice. A good example of this is Murder on the Orient Express. I think it was especially well done in that Poirot propounds two theories, one the misdirection which was intended and the other the true solution, and leaves it to the train manager to decide which to present to the police. In this way reason is used to pursue truth, and judgment is left to mercy. When Sherlock Holmes lets Ryder go free in The Blue Carbuncle, it lacks a little of this perfection because Holmes allows mercy to overrule truth, though I think it is made up for when Holmes points out that he is not retained by the police to remedy their deficiencies. Both because it is a good line, and because it does locate Homles’ mercy in the context of a fallen world that is not always strong enough to handle the truth well. The detective exists to restore the natural order, but in a fallen world that restoration must perforce be incomplete.
The other thing which this theory explains is why I so greatly dislike hardboiled detective fiction like The Maltese Falcon and The Big Sleep. (The Thin Man wasn’t as bad, but it wasn’t as hard boiled, either.) Chinatown (the movie with Jack Nicholson) was similarly awful. The detective does nothing to restore the right order injured by a misuse of intelligence. He just gets by, often by misusing his intelligence, and leaves the world as badly off has he found it, if typically not particularly worse, either. (Please note that all of the stories I mentioned were very skillfully told; they are very well done versions of what they are supposed to be. My objection is not to their execution but to their goal; to what they are supposed to be should not be done.)
I think that this theory of my friend is largely correct, and that it also explains why it is that those of us who love detective fiction love it so very much.