The genre of detective fiction has been enduringly popular since its inception in the 19th century, and continues to be so, as evidenced by the amount of shelf space devoted to it in popular bookstores.  Why do some people enjoy murder mysteries so much?  Because they appeal to two of the defining characteristics of our species:  we love stories and we like to think.

    But there is more to it than that.  Readers of detective fiction expect mystery writers to observe certain conventions.  There is a formula to these stories, and recognizing that fact can actually add to the readers' enjoyment as we see how cleverly the tale has been constructed within those guidelines.  It's like reading a sonnet: fourteen lines, two or three stanza forms, yet marvelous creativity sometimes flowers within that rigid format.

    Devotees of murder mysteries do not, of course, enjoy actual murder.  Au contraire!  We like order.  We like puzzles.  We like matching wits with the author who, if he or she has followed the "rules," has provided us with all the clues we need to solve the mystery—if we are clever enough and have not been distracted by the "red herrings" that have been dragged across the trail to send us in the wrong direction.  In many detective stories the murder victim is never even seen alive by the reader.  He appears only as "the body in the library" that sets the tale in motion.  All the interest is in the working out of the puzzle. 

    Maureen Corrigan explained the mystery reader's attachment to tradition in a Sunday, February 12, 2011 Washington Post book review:

A deserted mansion, a lonely churchyard, a village frozen in time.  Throw in a corpse or two and a dogged detective, and you have the outline for the traditional British mystery novel.  Detractors cry, "Formula," as if that were a flaw, but those of us who love the form know better.  Indeed, one of the greatest pleasures of reading a well-crafted mystery lies in recognizing the ways a gifted author rings changes on the basic pattern.

    One of the earliest precursors to the murder mystery is familiar to everybody.  It appears in Genesis 4: Cain's murder of his brother Abel, the Lord's inquiries, Cain's famous non-answer, his exposure and punishment. Leaving aside the theological issues, this ancient story has some of the elements of a murder mystery that still persist:  a dastardly crime that offends the social order; a really clever detective who identifies and interrogates the perpetrator; a villain who tries to evade responsibility for his crime; an appropriate punishment; the restoration of order.  What it lacks is the one crucial element that defines detective fiction:  the puzzle.  Everybody knows who killed Abel.

    The puzzle component is prominent in another example from early literature:  Sophocles' most famous play, Oedipus Rex.  As the drama opens, the city is devastated by plague.  A prophet announces that the gods are displeased because the late king's murder has gone unpunished.  Oedipus, the current king, announces that he will save the city by tracking down and punishing the murderer, no matter what it takes.  Oedipus is warned to let well enough alone, but in his pride rejects that advice.  Imagine his surprise and dismay when he learns the details of King Laertes' death and realizes that the murderer is—himself!  Even worse, he has married and fathered four children with his own mother.  The play is devastating in its portrayal of human misery and the folly of pride.  It also makes a wonderful detective story, with the unusual quirk of having the detective, Oedipus, find out that he himself is the murderer.  He administers his own punishment in a most grisly way, and again, order is restored.

    Another precursor of detective fiction in classic literature is Shakespeare's Hamlet: Hamlet learns in Act I, Scene 5 that his father, the King, has been murdered by his father's own brother, Claudius, who has not only usurped the crown, but has also married in unseemly haste Hamlet's mother, Queen Gertrude. As the officer Marcellus says early in the play, "Something is rotten in the state of Denmark." As with Sophocles, the tragedy also qualifies as a murder mystery, with Hamlet playing the detective, feigning madness, and even setting up a re-enactment of the murder scene, "Wherein I'll catch the conscience of the King."  This being a tragedy, all the main characters die in the end, but when the solution to the mystery is revealed, the rottenness is excised, a new king comes on the scene, and peace, we may hope, is restored to the kingdom. 

    Along with the puzzle, the restoration of social order is one of the primary requirements of detective fiction, particularly before the post-modern era.  A crime is committed.  The social order is disrupted.  The criminal must be discovered and punished.  It's a neat package.  Done well, it can be enormously satisfying. 

    The murder mystery genre as we know it began with Edgar Allen Poe and his stories about the fictional French detective Auguste Dupin, "The Murders in the Rue Morgue" (1841) and "The Purloined Letter" (1845). Dupin is probably based on the French detective Vidocq, founder and head of the French plainclothes unit La Sûreté, who published four volumes of hugely popular "memoirs" in the years 1828-29. To the modern reader, Poe's tales may seem ponderous, but the puzzles they pose remain gripping, and in them Poe invents many of the conventions of detective fiction that still obtain in the 21st century:  the eccentric, brilliant detective able to see and understand clues everyone else misses; the admiring assistant who functions as narrator and as stand-in for the reader; the dim-witted or unimaginative police who seize on the most obvious though erroneous conclusions; the wrongly-accused person; the sealed room; and the solution by unexpected means.  In these stories we first hear the axioms: "When you have eliminated all other possible explanations, the one that's left, however, unlikely, must be true," and "The more outré the crime, the easier it is to solve."  We also see in Poe's stories the trail of false clues laid down by the murderer and the clever ploy of hiding something in plain sight.  Arthur Conan Doyle picked up on all these tropes in the Sherlock Holmes stories.

    Those wildly popular stories began appearing in 1887 with A Study In Scarlet.  Eventually there were fifty-six stories and four novels, and they have been in print continually. Probably the best-known is The Hound of the Baskervilles.  Like most Holmes tales, it includes the paired characters introduced by Poe:  the brilliant, eccentric detective and his faithful companion.  Doctor Watson isn't really dim-witted; he's like us—smart and brave enough, but lacking the genius of his mentor.   As in Poe, there is a suspicious death, a set of baffling clues that seem to have no logical explanation, a limited number of suspects, several false clues, and an unlikely solution.  There is also a good deal of heart-pounding tension.   It seems at times as if the hound that menaces the moors must be a supernatural being.  But that is another rule of detective fiction:  no supernatural elements allowed.  The solution must be a rational one, as indeed proves to be the case here. 

    Many Holmes stories have been televised or made into movies; you can occasionally catch one on Turner Classics. The BBC series starring Jeremy Brett as Holmes is, in my mind, definitive.  BBC has a new series featuring Sherlock Holmes set in the 21st century, recasting some of the original stories in contemporary London, and has done amazingly well in transferring the essential Holmesian qualities into the modern world.

    From Doyle in the late 19th and early 20th centuries, we move into the "Golden Age" or "Classic" era of detective fiction.  There were many purveyors of the craft, none more popular or inventive than Agatha Christie (1890-1976).  In her sixty-six novels and fourteen stories, Christie used all the plot devices developed by Poe and Doyle and a good many more.  While she follows the unwritten "rules" of the genre (e.g., that all clues must be presented to the reader, that the writer cannot lie to the reader or use supernatural elements to solve the mystery), she pushes those conventions right to the edge.  Murder on the Orient Express is a good example.  The mystery unfolds on the luxury train from Istanbul to Paris, which runs into heavy snow, stranding the train.  In the night a murder takes place. No one can have entered or left the train, so the murderer is among a small group of people, all of whom, it develops, have a motive for the killing.  It is up to the famous detective Hercule Poirot to solve the mystery, which he does by interrogating everyone and employing his "little grey cells" to figure out the solution.  That solution is revealed in classic detective fiction style, Poirot assembling all the suspects and explaining his deductive process, finishing with the inevitable accusation of the guilty party—all the suspects have conspired to murder the victim.  In another famous Christie story, And Then There Were None, the murderer turns out to have been among the supposed victims, having in fact faked his death to avoid suspicion.  And in the most notorious example of pushing the limits of tolerance, in Who Killed Roger Ackroyd?, the narrator himself did the deed.
 
    In 1945, the literary critic Edmund Wilson's New Yorker essay "Who Cares Who Killed Roger Ackroyd?" blasted such unlikely plot devices and indeed the whole genre for being unbelievable and silly. While his criticisms are valid, he missed the point.  Part of the pleasure of reading these stories consists in admiring the author's ingenuity in coaxing the reader to suspend his or her disbelief as the puzzle unfolds.  When the author cannot do that, when the plot devices become too labored, the mystery just does not work.  With Dame Agatha, we're usually willing to go along for the ride, because the ride is so intriguing.

    On this side of the Atlantic the detective story took another turn, what we now call the American Hard-Boiled Detective Story.  This variation may have grown out of the corruption and cynicism of the Prohibition Era—dirty cops, mean streets—and also out of the cowboy tradition—the American hero as loner—moving west, beyond the reach of effete civilization.  The cowboy or detective hero rides into town, or accepts a case, and tackles the corruption flourishing there. Humphrey Bogart as Philip Marlowe is just a grittier version of Gary Cooper in High Noon.  Often the mystery deals with low-lifes—bums, petty criminals, mobster—but as the detective works his way into his case, often at the risk of his own life, the underlying mystery turns out to be rooted in the corrupt past and current dark doings of the upper class, that past often coming back to destroy the wrongdoers.  The detective is not necessarily a paragon of virtue.  Often he is a former cop who has washed out or quit in disgust and is now at odds with the law enforcement agencies, who themselves are peopled with corrupt and/or incompetent officers.  He is unmarried, perhaps divorced or widowed, has relationships with women that never work out, in part because he cannot commit, or feels no decent woman should be tainted by him.  He has turned private eye with a chip on his shoulder, operating on the edge, or slightly over the edge of the law.  He does business out of a dingy office, "on the 4th floor of the Acme Building," like Garrison Keillor's affectionate parody, Guy Noir.  There he sits, wondering how he's going to pay the rent, and waiting for a client.  Often that client is a beautiful woman with a mysterious past and a strange request. 

    Cue Dashiell Hammett's sleuth, Sam Spade.  If you haven't read The Maltese Falcon, you have certainly seen the movie version with Humphrey Bogart, and the movie gets it exactly right.  Hammett has created a memorable collection of truly disreputable characters, any one of whom would sell his grandmother for a candy bar, much less the fabulous treasure they are all pursuing, and for which they are willing to lie, cheat, steal, and, if necessary, kill.  For a while it seems as if Sam Spade himself is going for the main chance, but of course he is stringing the crooks along, as well as holding off the cops, until the mystery is all wrapped up and ready for delivery. It's a great story.

    Although it has its own conventions, the hard-boiled detective story fits the formula of mysteries in general:  a crime or series of crimes that disrupts the social order; the detective who is cleverer than anyone else and pursues the criminal doggedly; the inadequate police force; the string of clues discovered by the detective and laid out for the reader.  Absent is the dim-witted narrator, however. These stories are often told in the first person, so the reader looks at things through the eyes, if not the mind, of the detective.  The detective is a moral force, although it is a personal morality.  He may appear to be corruptible but turns out not to be.  The social order he restores at the end is small, specific, and temporary because he lives in a corrupt world.
 
    There have been many successors to Dashiell Hammett.  Among the best are Raymond Chandler and Ross MacDonald, both of whom wrote more fully developed and well-written mysteries.  In 1940, Chandler also published a marvelous critical essay called, "The Simple Art of Murder," in which he analyzed the detective genre, exposing many of its flaws, but ending with a passage that defines the hard-boiled school at its best:

But down these mean streets a man must go who is himself not mean, who is neither tarnished nor afraid.  The detective in this kind of story must be such a man. [...]  He must be [...] a man of honor, by instinct, by inevitability, without thought of it, and certainly without saying it. [...]  He is a relatively poor man, or he would not be a detective at all.  He is a common man or he could not go among common people.  He has a sense of character or he would not know his job.  He will take no man's money dishonestly and no man's insolence without a due and dispassionate revenge.  He is a lonely man and his pride is that you will treat him as a proud man or be very sorry you ever saw him. [...]  The story is his adventure in search of a hidden truth […].  (Chandler)

This passage describes, of course, the American hero, whether he appears in the guise of a detective, a cowboy, a soldier, an explorer—or even as a woman.

    In the early days of detective fiction, a woman sleuth would have been unheard of, but since the mid-20th century, women detectives have become more and more common.  Agatha Christie's Miss Marple is an early example.  In the United States, Sue Grafton's Kinsey Milhone  and Sara Paretsky's V.I. Warshawski are not only private detectives, but also belong to the hard-boiled school, and except for their gender, fit the gritty Sam Spade mold much more than the genteel Miss Marple one. Since the 1980s, female detectives of all varieties and female mystery writers have dominated the mystery market.  One of the most popular recent ones has to be Janet Evanovich's incompetent heroine Stephanie Plum, a big-hair New Jersey girl who works for her unsavory cousin Vinnie the Bailbondsman because she can't get a real job.  Stephanie works as a skip tracer, tracking down miscreants who have failed to show up for their court dates and hauling them off to jail.  Her misadventures and well as her love affairs make for hilarious reading, and yet, after all the dust has settled, she somehow solves the mystery.

    Women detectives and humorous mysteries are among the many, many variations that detective fiction has produced in recent years.  Whatever part of the country or the world you live in, whatever your hobbies and special interests, there is probably a mystery series related to it.  The detectives can be part of an organized police force, private eyes, amateurs, or accidental detectives.  What do they share?  Curiosity, persistence, method, logic, and a sense of justice.

    While much detective fiction can be filed under the heading "escape literature" or "entertainment," a significant and growing proportion of it cannot be so easily dismissed.  P.D. James and Elizabeth George write dark and densely plotted psychological novels that go way beyond figuring out "Who done it?"  As in any genre, there are excellent examples and a lot of junk.  You can usually tell the difference within the first chapter and act accordingly. 

    Graham Moore pinpoints the reason for the popularity of mysteries in his recent novel, The Sherlockian.  In detective fiction, says one of his characters, "we live in an understandable world.  We live in a place where every problem has a solution, and if we were only smart enough, we could figure them out." He continues:

"There needs to be something at the end, some sort of resolution.  It's not that the killer even needs to be caught or locked up.  It's that the reader needs to know.  Not knowing is the worst outcome for any mystery story, because we need to know that everything in the world is knowable.  Justice is optional, but answers, at least, are mandatory.  And that's what I love about Holmes.  That the answers are so elegant and the world he lives in so ordered and rational.  It's beautiful"  (Moore).

Chandler, Raymond. "The Simple Art of Murder". The Atlantic Monthly, December 1944.

Corrigan, Maureen. "The Usual Suspects, But Ingenious". The Washington Post, 12 February 2011: C3.