This fast vanishing art consists, in most instances, of a snowbound cottage, a comfortable box set complete with fireplace upstage right and a reliable chap in sensible shoes standing in front of a log 'n' flame effect rubbing his hands and saying "brrrr" a lot. This, or something very like it, reached its apogee in the hands of such leading thrill merchants as the urbane Francis Matthews and smouldering Gerald Harper, both of whom capitalised on their TV careers as Paul Temple and Adam Adamant respectively.
Those unfamiliar with the smartly-dressed style of the classic West End thriller as epitomised by Suddenly at Home, or anything by Francis Durbridge, should think Howard's Way with fewer boats and more blood. Unashamed, crowdpleasing moneyspinners, they appeal to conservative theatregoers and, when they work, nearly everyone's happy. Once upon a time, producers could rely on casting a couple of stars (Richard Todd? Nyree Dawn Porter?), issuing injunctions against the press about divulging the name of the rotter in question, watching audiences try to discover whodunnit, and counting the profits. And there were profits to be made. Richard Harris's The Business of Murder began in 1980 at the Strand, moved to the Duchess and wound up with an almost six year run at the Mayfair.
Anyone who believed the genre was dead and buried (or confined to The Mousetrap, 43 years and counting) will be surprised to learn that Dial M For Murder is back. The title is so familiar, half the world thinks it must have been written by Agatha Christie. In fact, it is one of a select band of plays the fame of whose titles eclipses that of the playwright. Who knows that before being catapulted to TV stardom as Private Godfrey in Dad's Army, Arnold Ridley wrote The Ghost Train, that cast-iron staple of repertory and amateur theatre companies up and down the land (as revived only last season to crowd-packing effect in a smart, programme-balancing move by Lawrence Till, artistic director of the Bolton Octagon). Twelve Angry Men, recently exhumed by Harold Pinter, is the work of Reginald Rose, while the man with his finger on the Dial is Frederick Knott.
This, his first play, was first produced for TV in 1952, the broadcast and its repeat five days later netting him pounds 141. The budget for the less- than-extravagant stage premiere that summer was 10 times the amount. Its West End success was repeated world-wide, although Pravda dismissed the Moscow incarnation as "a low-level bourgeois gutter play". Hitchcock's film version - shot in a mere 36 days and in 3-D to boot - kept faith with the conventions of the piece by holding on to Knott's structure and not falling into the trap of opening the play out and thereby dissipating the tension.
Unlike Christie's pot-boilers with their hidden evidence, Knott's play isn't a whodunnit at all. Very early on, we become privy to the fact that the tennis-playing hero has plans for his wife that don't include the word "love". Instead, Knott trades in plot twists and builds suspense while working the tried and trusted formula of marriage, money and murder.
The play's return is being heralded with a predictable chorus of groans. Thrillers were enough of a West End mainstay to inspire one of Tom Stoppard's neatest comedies, The Real Inspector Hound, almost 30 years ago. Now, they are deeply unfashionable: who can remember the last good one? Sleuth? In 1970, Anthony Shaffer, brother of the more famous Peter, notched up a five-year London run with his fiendishly plotted winner, which managed to satirise the Christie country-house genre while serving up a storyline complicated enough to satisfy the most exacting of audiences.
Broadway has given us Ira Levin, with Deathtrap his most successful theatrical outing. "You really were on the edge of your seat," recalls one audience member. "There was a terrifying moment when someone came crashing through a window. That's what you go for: action that you don't expect to happen, the shock." She wasn't too impressed by the chopping-off of Bill Paterson's leg in the stage version of Stephen King's Misery, "but I'll never forget the moment Sharon Gless was suddenly revealed in the doorway in a shaft of light".
Stephen Mallatrat clearly understands that the thriller audience wants a good story. His adaptation of Susan Hill's The Woman in Black is now in its eighth year, while last year's Dead Guilty - reviews for which included such choice phrases as "a perfect anaesthetic" and "an irredeemable dud" - not only ran its initial six-month period but was extended for a further three. Unlike New York, where attendances and box-office receipts are published weekly, West End figures are a closely guarded secret but, like The Mousetrap, Dead Guilty was certainly working on the premise that what you lose in the week, you make up for at the weekend.
Don't be fooled, however, into thinking that the thriller is easy money. An overdesigned version of Christie's Murder Is Easy from the team behind TV's Poirot sailed in to the Duke of York's in 1993 with a cast including Richard Attenborough's daughter Charlotte. If The Mousetrap was good enough for her dad (he was in the first cast) then this, by implication, was good enough for her. It was not long for this world. The salient point here is that not only did this production-team work better on TV - Poirot has won Baftas like they're going out of style and sells worldwide - but that TV has usurped the entire genre. Who wants to see creaky old stagecraft when you can have Joan Hickson in lovingly crafted versions of Miss Marple that paper over the cracks by taking the work seriously? Armchairs, for an elderly audience, or any audience for that matter, are a great deal more comfortable than most theatre seats. If they do venture out, well- filled wallets at the ready, maybe they would concur with Blanche in Belle Reprieve, the Split Britches / Bloolips spin on A Streetcar Named Desire, who bursts out of an experimental scene to harangue the cast: "What's wrong with a beginning, a middle and an end? I want french windows and a drinks trolley."
As the population ages, there may be an ever-increasing case for giving audiences what they want. The issue, of course, is one of balance. The West End cannot (and should not) survive without the "boulevard bon-bons" referred to by Trevor Nunn in his recent tirade about the state of London's theatre, but it has to be balanced by work of vision, immediacy and excitement. The irony about going to a murder mystery is that it is theatre at its most deadly. Sponaneity is nowhere. Everything is subservient to plot. You derive the same satisfaction from watching a thriller as from completing a crossword puzzle. After the chaos of murder, order (usually set in nice polite society) is restored. Reassurance as an art form.
"Twenty-seven West End theatres are at present offering light comedies and musical shows, of which perhaps a dozen are good of their kind. The number of new plays with the slightest claim to serious discussion is three." Kenneth Tynan wrote that in 1954. Sound familiar?
If theatre is to survive, it has to offer something that TV cannot. There must be hundreds of people who have turned up to Stephen Daldry's production of An Inspector Calls who have found themselves watching something owing more to expressionism and ideas of socialism than anyone's idea of a detective story. Many will have liked it but, even if you loathed it, Daldry and designer Ian MacNeil have turned an old warhorse into something fresh and stimulating. Will Dial M for Murder manage that? In theatre's dwindling audience is there anybody left who knows that telephones used to have letters as well as numbers on them?
n 'Dial M for Murder' is in preview at the Apollo Theatre, London W1. Booking: 0171-494 5070