I'm going to restrict my answer to the murder mystery genre. Crime and Punishment is a truly great novel about crime, but is way beyond the scope of this piece! So here goes...
A convincing, likeable detective is one answer. A tour round the world of current crime fiction will reveal a bewildering selection of sleuths. Policemen, of course – my favourites are the team from Ed McBain’s 87th precinct – but if you prefer you can have your murder solved by Jane Austen or a cat.
Must the detective be likeable? I think the answer is ‘yes’. They can be flawed, of course, as we all are. They also start with a moral advantage over other characters in the book, as they have a passion for truth. But I’m not sure that this alone will keep us rooting for him or her.
A good setting matters, too. As with any good writing, quality crime fiction oozes a sense of place. I’m not sure any crime novel has ever beaten Dorothy L Sayers’ The Nine Tailors for this, though as an East Anglian, maybe I’m biased.
Setting can also mean backdrop – historically significant events, for example. Anthony Horowitz’s Foyle's War TV series is a great example.
An ingenious murder is another big plus. I’ll never forget my first Crime Writers Association conference, which was held in Pitlochry. We visited a whisky distillery, and my colleagues spent most of the tour muttering things like ‘Ooh, I could have someone pushed into that vat’ or asking the guide for ever more detail about a set of rotating blades that did something with barley. (They were delightful people, by the way, putting their dark imaginations to positive use entertaining the public.)
In the end, however, what drives a great crime novel is a sense of ever-rising puzzlement in the reader. Every lead seems to make the situation less clear, not more. The moment a possible backstory looks to be true, something crops up to render it impossible. (The murder of the main suspect, half way through the story, is an overused example of this.) Nothing is ever, ever as it seems. ‘Curiouser and curiouser’ is the motto.
Every suspect should have their moment, the time when it looks like they are the perpetrator. I find it helps to look at the story as a kind of race between teams – Dr X’s supporters vs. the chambermaid’s vs. the vicar’s (or whatever). Each one should have their moment in the sun, when the turn of events suddenly points to them, and makes their team celebrate. ‘We are right!’ Five pages later, of course, things are less obvious…
However everything that happens in these apparently shifting realities has to be consistent, with what has gone before and with what will happen in the end. It must also be consistent with human nature (or at least with the nature of the individual characters). Great crime fiction is intricately plotted, but never ‘plot-driven’, in a way that makes characters do unlikely things because the plot demands it.
The crime writer walks that dizzy line between giving the reader as little information as possible but as much as is necessary. That’s an art in all storytelling, of course, as Chekhov understood so well when he said that ‘If in the first act you have hung a pistol on the wall, then in a following one it should be fired.’ (I don’t know if he offered similar advice about lead piping or candlesticks.) The crime writer must master this.
He or she toys cruelly but tantalizingly with the truth – but only for a while, as in the end, the writer is its servant: the genre demands that finally the real story be told. At the climax, the moment of realization, the reader of the perfect crime novel slaps their forehead and says ‘Of course! Why didn’t I see that earlier?’ (Unless 'their' suspect wins, when it’s a simple shout of ‘I knew it!’ – but in a relieved tone; it’s not a bored, ‘I’ve known since page 43’ voice.)
The Big Reveal was easier in the ‘Golden Age’ of crime fiction, which was between the two world wars, when (mainly female) writers like Sayers, Agatha Christie and Ngaio Marsh delighted readers. Often the detective would gather all the suspects and give a kind of speech. ‘At first I suspected the butler, but then I realized that the Colonel could not have heard the dinner gong from the West Wing…’ This doesn’t wash with modern audiences, but the story must out, in full. A confession is still the best way, but it has to convince – another difficult ask, as real bad guys often keep their secrets as their last piece of power.
At the end, the reader must be left with that ‘Wow’ feeling, of having been teased, baffled and delightfully tricked, and then given an emotionally rich and rewarding story of what really did happen – all, of course, in a setting to which they have been taken as memorably as if they’d been there in person.
An impossible task? No, because great crime novels have been written. An incredibly difficult one? Oh, yes – which is why writing in the genre is such a brilliant challenge.