Why Sherlock Holmes Beats CSI Any Day

It's forensics and DNA that have caused all the trouble. Time was, anyone could solve a murder in a detective novel, which meant just about anybody could have a go at writing one. Your detective could be an effete aristocrat like Lord Peter Wimsy or a bohemian intellectual with a coke habit, like Sherlock Holmes. She could be a deceptively ditsy old lady like Miss Marple, or even a moustachio'd Belgian; the important thing was that he or she should not be a member of the official police force.

Indeed, before I came to write my first crime thriller, Heresy, the murder mysteries I had loved when I was growing up featured old-style detectives who were usually pitted against the incompetent and bumbling forces of the law. More often than not, these buffoons threatened to scupper the investigation with their wrong-headed and stubborn love of procedure over intuition, and ended up humbled by the hero or heroine's superior little grey cells. This tradition of the maverick outsider battling not only the enemy but the authorities who ought to be on his side persists in the likes of 24's Jack Bauer, but the much-loved amateur sleuth has sadly been elbowed aside by the supremacy of science.

Once real detective work came to rely on forensics and pathology labs, the ability to distinguish between ninety-seven different blends of tobacco just by sniffing the ash somehow lost its value. The gimlet-eyed observer, peering out from behind newspaper or knitting to spot subtle clues overlooked by unimaginative policemen, was replaced by the postmortem, the toxicology report, the SOCOs clad from head to foot in plastic bags with their swabs and test tubes.

Not only did this development make life difficult for the genteel amateur detective, it really upped the ante for anyone who fancied writing a detective novel. The only people who could convincingly solve murder cases now were real police officers or pathologists or forensics experts, and if you want to create a plausible character who does that for a living, you'd better know what you're talking about. Crime readers are very discerning, and they don't have much patience for bluffers who don't do their homework properly.

I'd always wanted to have a go at writing a murder mystery, but there was no way I could ever find the time to work as an intern at a police HQ or a pathology lab, even if they let complete strangers in to do that sort of thing, which I doubt. Fortunately, there is a solution for those of us who lack the enthusiasm for the technicalities of a postmortem, and that is simply to turn back the clock. Turn it back far enough, to the days before detection was all about science, and you are free to reintroduce the non-professional sleuth, living on his or her wits.

Sixteenth-century England seemed to me the perfect period to set a smart outsider to work solving a series of shadowy murders. With the Protestant queen Elizabeth on the throne and the Catholic powers of Europe keen to see her removed by whatever means and England brought back to the Roman Church, the air was thick with conspiracy theories, assassination plots, suspicion and betrayal. Catholic priests and would-be killers arrived from mainland Europe in an array of enterprising disguises, and the government had its hands full trying to monitor the coastline and ports for potential subversives.

Hardly surprising, then, that this period gave birth to modern espionage, in the sense of an organised and centralised intelligence service. Sir Francis Walsingham, Elizabeth's Secretary of State and spymaster, created a network of undercover agents and informers recruited from every walk of life to observe and report any signs of unrest. When I read that the Italian philosopher Giordano Bruno may well have been on Walsingham's payroll, I knew I had my hero.

Of course, historical novels require a considerable degree of research as well, but happily it's the kind you can do in libraries or wandering around old buildings, and you don't need to be wearing a sterile bodysuit. But in many ways it's wonderfully liberating, and allows more freedom of imagination when it comes to the murders, too. Rather than having to think, 'Ah, yes, but the killer would have left fingerprints,' you can answer yourself, 'yes, but they didn't have fingerprints in those days, never mind DNA profiling.' Both murderer and detective are free to be a lot more ingenious than the rigours of modern science allow.

Perhaps the increasing popularity of historical thrillers at the moment marks a nostalgia for the old-school amateur detective, independent of the law, relying on good old-fashioned powers of deduction rather than a sophisticated chemistry set. It's certainly a lot more fun than being stuck in a lab.