In her novels, stories and stage productions, Agatha Christie rang every possible change on the standard whodunit to keep her readers guessing—usually incorrectly.

However one-dimensional her characters, however thin her style, however unrealistic her crimes and criminal setting, Christie forged her fiendishly clever plots into more classic mysteries than any author since Arthur Conan Doyle, and became arguably the world's best-selling writer. In fact, her weak understanding of character, style and criminality in the real world may have been essential for her success.

Christie had the great knack of being able to resolve a mystery by landing on a culprit who had been unsuspected but who, after the revelation, seems exactly right. "It was there in front of me the whole time and I didn't see it," the reader is thrilled to feel at the conclusion of Christie's best works with their extraordinary solutions.

Having raced through the page-turner to get to the end, the reader never questions: "But is this really a person who could commit murder and keep up a convincing acting job before family, friends, lovers and intense investigators all this time? Is this how a clique of real people would react if a murderer were loose among them? Is such a ridiculously convoluted crime ever carried out in reality? Could such a killer actually be found by a private or amateur detective, where police have failed, by a rational sifting of clues? And is it indeed really so rational—or just lucky guesses?"

Any comparison with crime in the real world, or even with crime in the works of more grittily realistic crime writers, would make Christie's stories fall apart. But her fans don't care to make that comparison. A Christie novel is a gigantic puzzle to be worked on, clues are to be assessed, the deft insight of the investigator is to be marvelled at—all within the small, pretend world she sets up.

And it usually is a small society indeed where the mystery unfolds: visitors to a country manor, inhabitants of a tiny village, vacationers at a exotic resort, residents of a snowed-in lodge, passengers on a train or boat, guests on a remote island....

Christie didn't invent what the British came to call the cosy mystery, with a small group of suspects-to-be thrown together in an isolated setting for a rather bloodless crime, which is investigated like a sort of parlour game. One thing you can be sure of in this sub-genre, the killer will never turn out to be a passing madman, a member of a villainous gang, or anyone else outside the proscribed set of socially entwined suspects. Whodunit is reduced to which-one-of-them-dunit. Christie didn't invent this sub-genre but she developed it without parallel.

Raymond Chandler had Christie and her English colleagues in mind when he wrote his devastating critique of their entertainments in his essay "The Simple Art of Murder":

There is a very simple statement to be made about all these stories: they do not really come off intellectually as problems, and they do not come off artistically as fiction. They are too contrived, and too little aware of what goes on in the world.

He picked Christie's best-known Hercule Poirot mystery, Murder on the Orient Express (1934), as one example of a particularly implausible bit of detection with a solution "only a halfwit could guess". Of course, that didn't keep it from becoming one of the most popular of all mystery novels and the basis for continually popular films.

Changing the ground rules

Murder on the Orient Express is one of Christie's plots with a famously maverick conclusion, dashing first-time readers' expectations of what kinds of solutions are acceptable in a mystery novel. Her other most enduring mysteries also have final plot twists unlike anything found in other writers' works: The Murder of Roger Ackroyd (novel, 1925), And Then There Were None (novel first published under a different title, 1939), The Mousetrap (play first presented in 1952) and a couple of others.

Some critics and a few readers cried, "Unfair!" at the time of each such work, charging Christie was breaking an unspoken contract between writer and reader about the mystery's ground rules.

But many more found it deliciously innovative, expanding the mystery's possibilities. And time has turned these titles into standards. The Murder of Roger Ackroyd was named the best crime novel of all time by the UK's Crime Writers' Association nearly nine decades after publication. And Then There Were None is claimed to be the world's top-selling mystery novel, with more than a hundred million copies bought over the past eighty years. Nearly seven decades after its premiere The Mousetrap is still on stage in London, England, the longest such run in theatrical history.

Outside those rule-breaking milestones, her publications, starting with the novel The Mysterious Affair at Styles (1920), taken as a group are generally decent mysteries, well structured and with unexpected denouements. Some better than others, but as a whole not significantly better than her contemporaries' works. Individually they range from clever and engrossing at their best to plodding, predictable and repetitive at their worst, particularly among her late efforts. Most suffer from the aforementioned superficial characterizations, implausible plots, and pedestrian writing.

This goes for all her mystery novels and stories, whether they involve her famed fictional crime solvers Poirot and Jane Marple, the less successful Tommy and Tuppence, or her one-off mystery dwellers.

When her writings tip into international intrigue, her weaknesses are all the more evident. Her formula just doesn't work for thrillers. Her efforts don't seem to have the minimal connection with the real world that even the most escapist of such fiction needs.

When Christie's fans open one of her crime detection pieces, they are accepting the author's premises, however different from those of real crime. They are conspiring in a puzzle that can allegedly be solved with close attention to clues scattered through a story of relationships among a group of people. They're engaging in a small internal world, with its own laws and conventions, outside reality be damned. When you start working out a crossword puzzle, you don't question whether it ever happens in life that words fall together in patterns so easily, or how it is these clues are lined up so neatly to define the words you're looking for. It's just how the game is played.

In each puzzle she creates, it's important that Christie provide just enough personality for each character and attribute just enough reality to a bizarre crime to make the story hook the reader. She needs to use the fewest number of words to advance the plot, yet in a colourful fashion, to keep the reader going. She needs to conclude with a solution that gives the illusion of being one that any sharp reader could find—but doesn't. The reader accepts all this. And that's how her game is played.

It's how it is played by many a mystery writer and their fans, before, during and after Christie's time. But on the whole, and throughout her career, Christie has pulled it off more consistently than most of them. And that handful or more of truly groundbreaking twist endings, raise her well above others who play her particular puzzle-solving game.

Now, the cozy puzzle is not the only game around. The American hard-boiled private detective style developed by Chandler and others, the more literary and psychological approach of Christie's successors like P.D. James, the police procedural followed by many crime writers of the past half-century, and the ever-popular noir novel of sex, violence and amorality—revived most spectacularly by Nordic writers in recent years—these are all competing for readers today. And readers enter these worlds with different sets of assumptions and expectations.

But enough still want the pure, unreal puzzle that Christie offers. Enough still want to be pleasantly challenged and satisfyingly surprised at the puzzle solution—enough to keep her books selling by the millions each year.

And, whether I like it or not, that took a kind of genius on Agatha Christie's part.

— Eric

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