What is surprising is not that the detective story has altered but that it has survived, and that what we have seen since the interwar years has been a development, not a rejection, followed by renewal. Crime fiction today is more realistic in its treatment of murder, more aware of scientific advances in the detection of crime, more sensitive to the environment in which it is set, more sexually explicit and closer than it has ever been to mainstream fiction. The difference between the crime novel in all its variety and detective fiction has become increasingly fudged, but there still remains a clear division between the generality of crime novels and the conventional detective story, even at its most exciting, which continues to be concerned with each individual death and the solving of the mystery through patient intelligence rather than physical violence and prowess.

I find it interesting that the detective hero, originated by Conan Doyle, has survived and is still at the heart of the story, like a secular priest expert in the extraction of confession, whose final revelation of the truth confers a vicarious absolution on all but the guilty. But, not surprisingly, he has changed. Because of the growing importance of realism for writers and readers, in part arising from the comparative reality of television series, the professional detective has largely taken over from the amateur. What we have are realistic portrayals of human beings undertaking a difficult, sometimes dangerous, and often disagreeable job, beset with the anxieties common to humanity: professional jealousies, uncooperative colleagues, the burden of bureaucracy and difficulties with wives or children. An example of the successful professional detective at peace with his job is Ruth Rendell’s Inspector Reginald Wexford, who, so far from being a disillusioned maverick, is a hard-working, conscientious, liberal-minded police officer, happily married to Dora, who provides for him that stable background which helps to buttress him against the worst traumas of his daily work.

And policing itself has changed dramatically. In the Golden Age, police forces were not yet integrated into the forty-two large forces of today, and major cities and their county were separately policed. This gave opportunities for productive rivalry as each strove to be the more efficient, but the separation was economically expensive and could cause difficulties in co-operation and communication. Chief constables, so far from coming up through the ranks, were usually retired colonels or brigadiers, experienced in leading men and promoting loyalty to a common purpose but occasionally over-authoritative, and representative of only one class. But they were able to know individual officers and were known by them, and both they and the policemen on the beat were familiar and reassuring figures to the much smaller and homogenous community they served. The job of policing our multicultural, overcrowded island and its stressed democracy is fundamentally different from the job in, for example, the twenties and thirties. I remember as an eight-year-old being told by my father that if ever I were alone and afraid or in difficulties I should find a policeman. Police officers are as ready to help a child in distress now as they were then, but I wonder how many parents in the more deprived inner-city areas would give that advice today. The crime novelist today needs to understand something of the ethos, ramifications and problems of this rapidly changing world, particularly if his detective is a police officer.

The Watson in the form of a sidekick, created to be less intelligent than the hero and to ask questions which the average reader might wish to put, has long since bowed out and, on the whole, to general relief. But the detective, whether professional or amateur, does need some character in whom he can rationally confide if the reader is to be provided with enough information to be engaged in the solution. For a professional detective it is usually the detective sergeant, whose background and personality provide a contrast to that of the hero and an ongoing relationship which is not always easy. The reader becomes involved in the sergeant’s different domestic background and different view of the job itself. Notable examples are Colin Dexter’s Morse and Lewis, Reginald Hill’s Dalziel and Pascoe, Ruth Rendell’s Wexford and Burden, and Ian Rankin’s Rebus and Siobhan Clarke, where we have the added advantage of a woman’s point of view. In the hands of such masters of the detective story they are subordinate to their boss in rank but not in importance. It is not surprising that Morse has been successfully replaced by Lewis, who has grown in authority since his promotion and now has a very different, more intellectual subordinate of his own, Sergeant Hathaway, to fulfil the function that was previously his.

A. A. Milne had a passion for detective stories, although he didn’t persist in writing them, and is best known for The Red House Mystery, first published in 1922. In a reissue of the novel in 1926, he wrote an entertaining introduction in which he addressed the issue of the Watson.

Are we to have a Watson? We are. Death to the author who keeps his unravelling for the last chapter, making all the other chapters but prologue to a five-minute drama. This is no way to write a story. Let us know from chapter to chapter what the detective is thinking. For this he must watsonize or soliloquize; the one is merely a dialogue form of the other, and, by that, more readable. A Watson, then, but not of necessity a fool of a Watson. A little slow, let him be, as so many of us are, but friendly, human, likeable…

“Friendly, human, likeable,” an accurate description of the Detective Sergeant Watsons of today, and long may they flourish.

Writers of the Golden Age, and indeed for some decades after, were little concerned with forensic or scientific research. The present system of forensic science laboratories was not yet in prospect and few of the victims were subjected to an autopsy, or if they were, this unpleasant procedure was seldom mentioned. Occasionally a postmortem was undertaken by the local general practitioner, who within hours was able to inform the detective from exactly which poison the victim died, a feat which would occupy a modern laboratory for some weeks.

The discovery of DNA is only one, but among the most important, of the scientific and technological discoveries which have revolutionised the investigation of crime. These include advanced systems of communication, the scientific analysis of trace elements, greater definition in the analysis of blood, increasingly sophisticated cameras which can identify bloodstains among multi-stained coloured surfaces, laser techniques which can raise fingerprints from skin and other surfaces which previously offered no hope of a successful print, and medical advances which affect the work of forensic pathologists. Modern writers of detective fiction need to be methodical in their research and the results integrated into the narrative, but not so intrusively that the reader is aware of the trouble taken and feels that he is being subjected to a brief lesson in forensic science. Some novelists manage so well without the inclusion of this scientific knowledge that the reader doesn’t feel the lack of it. I can remember only one instance in which Morse mentions a forensic science laboratory but, reading the books or watching the televised adaptations, we never for a moment suppose that the Thames Valley Constabulary is bereft of this necessary resource.

I like to do my own research, as do most detective novelists, and am grateful for the help I have received over the years both from the Metropolitan Police and from the scientists at the Lambeth Laboratory. But there have been mistakes. These usually arise, not from facts about which I am ignorant, but from those which I fondly and mistakenly imagine I already know. In one of my early novels I described a motorcyclist, disguised by his oilskins and goggles, “reversing noisily down the lane.” This led to a letter from a male reader complaining that, although I was usually meticulous in my choice of words, the sentence gave the impression that I thought that a two-stroke motorcycle could go backwards. So indeed I did. This mistake proved expensive, leading over the years to much correspondence, invariably from male readers, sometimes explaining in minute detail and occasionally with the aid of a diagram precisely why I was wrong. Salvation came some years ago in the form of a message on a postcard which said simply, “That motorbike-it can if it’s a Harley-Davidson.”