IN 1860, A CHILD WAS FOUND murdered and stuffed down the privy of a country house in Road, Wiltshire. Such was a usual destination for illegitimate infanticides, but three-year-old Savill Kent was a wanted, even spoilt child. Worse, his family was middle-class, and the killer was clearly someone from the Victorian sanctum, his family home. A sensational media storm ensued, affecting the Kent family, the police, and the course of English detective fiction.

The Road Murder is an enduring true crime mystery. At the time all England was voyeuristically intrigued as to whodunit. Additional information emerged over the decades, as have a series of books devoted to the crime. Kate Summerscale's is the latest in a long progression, which began in 1861, with the post-mortem doctor. All have extensively examined and re-examined the evidence - but none has solved the case conclusively.

Summerscale, who last week won Britain's Samuel Johnson prize for her book, effectively depicts the crime, its aftermath, and the conflicting theories. Some might argue for more modern psychology, or criminology - particularly of the circumstances in which small children are murdered. She does not introduce startling new evidence, although she does enlighten various obscured aspects of the case.

First suspect was nursemaid Elizabeth Gough, who slept in the nursery. Charles Dickens privately opined she had been "intriguing" with the child's father, Samuel Kent. Savill, waking and witnessing "blissful proceedings", was killed to ensure his silence. Samuel Kent implicated his teenage daughter, Constance, the child's stepsister. He claimed his first wife had gone mad after baby number four (which did not, appallingly, prevent another six pregnancies). Thus was the crime explained: Constance had inherited her mother's illness.

Summerscale makes the investigating detective, Scotland Yard's Jonathan Whicher, her hero. She is slightly hindered by the fact of no surviving images; also that Whicher, when he lacked evidence, would bluff or harass a suspect into confession. Thus Constance spent a week in jail, with no results. She would confess five years later, yet details of her testimony were wrong, suggesting innocence. Her youth spared her the gallows, but she received 20 years imprisonment.

On release Constance disappeared, but emigrated to Australia. She trained at The Alfred hospital in Melbourne and had a significant career in nursing. Her long life here was worthy and blameless. Only once did she break her silence, writing an anonymous letter that depicted the Kents as truly horrific. The first Mrs Kent had not been mad, but maltreated; as were her children, particularly Constance; and the family was riddled with syphilis.

Such was strong stuff, too sordid and gory for Victorian tastes. Some elements of the case reappeared in Wilkie Collins' The Moonstone, considerably toned down. Like Whicher, Collins' detective Cuff failed to crack the case. While Summerscale sees Whicher as inspirational, his work at Road arguably had a negative effect on crime fiction.

For the Victorians, police were problematic, unheroic because of their low-class status. The police procedural as we know it did exist, but its protagonists tended to be middle-class or distressed gentlemen. Dickens' Bucket in Bleak House is not the central figure, nor the novel's hero.

One exception was Mary Braddon's 1860 The Trail of the Serpent, featuring a lively but mute working-class detective, Peters. It is not mentioned by Summerscale, despite being reprinted in 2003 as the "first English detective novel", with an introduction by Sarah Waters, who also blurbed this book.

The Trail appeared in the same year as the Road murder. It is significant that Braddon immediately afterwards reverted to gentlemanly amateur detectives, as did detective fiction generally. Conan Doyle's

Holmes, for instance, is amateur - and smarter than the professional police. Only in the 20th century did class prejudices relax.

It was Constance, rather than Whicher, who proved the real fascination of the case. Beyond the true crime books, she has appeared in fiction and poetry, with the most novel interpretation being Francis King's Act of Darkness (1983) in which Gough and Constance were lovers. It was no worse than Summerscale's conclusion, that Constance and her brother William were joint murderers.

Constance's confession freed William from suspicion, and enabled a career in science. He adopted his dead brother's name - bizarre if he was the killer - becoming William Saville-Kent. In Australia he became a noted marine biologist, and his naturalist books were published in London.

The Kent siblings, in our modern world, would write misery memoirs. They endured terrible trials, but made significant contributions to Australian life. Such would indicate that juvenile offenders, no matter how foul the crime, can be successfully rehabilitated.

The jury remains out on their guilt, but either way they are a testimony to the strength of the human spirit.