Over the years, many attempts have been made to prescribe "rules" for writing crime novels. Tongue in cheek, Ronald Knox devised a "detective story decalogue" in 1929, insisting, for instance, that "no more than one secret room or passage is allowable" and even that "no Chinaman must figure in the story". Scarcely more useful was Sutherland Scott's recommendation in 1953 that "it is dangerous to create too much sympathy for the criminal". Today, perhaps, the only rule is that there are no rules. Given the diversity of the genre, to set down a list of "do's" and "don'ts" is a pointless exercise. This short article simply collects a few of my own thoughts, focused mainly on the writing of whodunits.

A good starting point is to remember that a crime novel must entertain. If it fails in that objective, then for me it fails altogether, however polished it may be in terms of literary style. Plot matters, but characterisation and atmosphere are equally important the days when readers of crime novels would put up with 300 pages of lifeless prose, as many did in the years between the two World Wars, are gone and those writers who concentrated on plot alone are now forgotten. Is Agatha Christie, often criticised for her "cardboard characters", an exception? I think not. Christie's detractors undervalue her lightness of touch and also the skill with which she describes, however simply, recognisable human types. She also had the ability to ring the changes: Death Comes As The End, for instance, is set in Ancient Egypt. Those factors, just as much as her mastery of plot, account for her continuing success.

Many fine crime novels, such as those by Barbara Vine, lack a conventional detective character. Nevertheless, series detectives have had reader appeal ever since the days of Sherlock Holmes. Miss Marple, Lord Peter Wimsey, Philip Marlowe, Maigret and Chief Inspector Wexford are all as celebrated as their illustrious creators. So it is worth considering the possibility of creating a detective who can re appear in later books if the first is a success. I did this with my lawyer sleuth Harry Devlin and I also took the precaution of making him a youngish man, in the hope that the series might run and run.

Where to start with the plot? Usually, I prefer to begin at the end. With my first novel, All The Lonely People, I set myself the task at the outset of dreaming up an interesting murderer, victim and motive. After that, came the means by which Harry Devlin might discover the truth about the crime. Then I turned my attention to the other suspects, red herrings and clues the elements which contribute to the texture of the finished work. The book earned a nomination for the John Creasey Memorial Award for the best first crime novel for 1991 and, duly encouraged, I sought to build upon that foundation in my later novels about Harry Devlin, whilst striving to avoid the dangers inherent in writing to a formula. One of the joys of a series is that it provides a sound framework which affords plenty of opportunity for experiment.

A sense of place is crucial for most crime writers. Consider the work of novelists as distinctive as Raymond Chandler and P. D. James. Who can deny that the Oxford setting is an integral part of the appeal of Colin Dexter's immensely successful series about Inspector Morse? It seemed strange to me that Liverpool has not formed the background to more than a handful of mystery novels. After all, it is a rather more credible scene of serious crime than the city of dreaming spires. When I started work on the Harry Devlin series, therefore, I had no hesitation in opting for a Merseyside background. Many readers seem to prefer books set in readily identifiable locations to those which take place in, for example, fictitious Home Counties villages. The risk of setting a story in a real village, town or city, however, is that of libel. Since, oddly enough, the law provides that libel can be committed unintentionally, it makes sense to do one's best to avoid too many resemblances between fictitious characters and incidents and those in real life.

Writing a crime novel is hard work, but there is no need to be unduly daunted by the task. It helps to bear in mind that if your story does not entertain you, it is unlikely to entertain anyone else. If you do not enjoy reading crime fiction, then it is probably a mistake to try to write it. Pleasure, rather than profit, should be your main aim. If you do like to while away the time by reading the work of crime writers past and present, you will be able to learn a good deal from them. And perhaps, in the long run, you may even find that crime really does pay ...