In the postscript to The Suspicions of Mr Whicher, Kate Summerscale quotes an observation made by Raymond Chandler in 1949. “The detective story,” notes the master, “is a tragedy with a happy ending.” On Tuesday night, Summerscale discovered just what Chandler was talking about when she won the BBC Four Samuel Johnson Prize for Non-Fiction, and £30,000, for her own detective story — a rich and gripping account of the Road Hill Murder of 1860.

Summerscale beat off stiff competition, particularly from The World Is What It Is, Patrick French’s pungent biography of VS Naipaul, and Tim Butcher’s courageous travel memoir, Blood River: A Journey to Africa’sBroken Heart. That she did so is testament not only to a writing style that imitates the great Victorian detective novels, but to the magnetism of the “complex, shabby” character at the centre of her account, Jack Whicher.

Through Whicher, one of the first Scotland Yard detectives, we learn about the Road Hill Murder, in which a four-year-old boy, Saville Kent, was brutally suffocated, cut, stabbed and finally hidden in the outside privy of a middle-class family home in Wiltshire. The story of Saville gripped the nation, and broke Whicher, as theory and countertheory were espoused and destroyed.

Summerscale, a former literary editor of The Daily Telegraph, gave up work in 2005 to concentrate on The Suspicions of Mr Whicher. Ten years ago, before becoming a mother, she wrote The Queen of Whale Cay, a well-received biography of the decidedly bonkers “Joe” Carstairs, a British woman who governed her own island in the West Indies. Summerscale’s decision to become a full-time author was described by her friends as “brave”, by which, she says, “they meant ‘stupid’ ”.

Times Archive, 1860: The recent murder at Road-hill House

A crime has just been committed which for mystery, complication of probabilities, and hideous wickedness is without parallel

• Leading article: Road child murder

• The case of Constance Kent

• Constance Kent indicted

Related Links

• Whodunnits? A cultural religion

• Unsolved murder helps author win top prize

• The Suspicions of Mr Whicher by Kate Summerscale

Does it feel good to have one’s bravery favoured with fortune? “It feels great,” says Summerscale, whose blonde curls, appropriately enough, give her the look of a Dickensian heroine. “I had a wonderful night — it was shocking to win. I have no idea what to do with the money. I think I’m going to spend it on an Italian meal in Hampstead for my family on Saturday, then we’ll see.”

What drew her to the Road Hill Murder? “When I first read about this case, in a book of famous crimes of the 19th century, I was immediately drawn to the seamy gothic elements — the family story about insanity, adultery and wayward adolescent children. But what made me think I could write about it was this character, Jack Whicher. I could see this story was about detection as an idea — about its roots in Victorian society. It was about being a detective as a profession, and the explosion of detective fiction in the mid-19th century, particularly that of Wilkie Collins, Dickens and Edgar Allan Poe. It had to be about more than the crime, however gripping I found it personally.”

The Suspicions of Mr Whicher is, Summerscale explains, a book fascinated by the intersections of Victorian fiction and society. Indeed, the expectations of Whicher were largely born out of what the public had read in the flowering detective genre. Meanwhile, the Road Hill case fed back into that genre, inspiring a slew of fictional imitations.

It became the original country-house murder mystery.

What is most striking about her account (and this, perhaps, is what won the judges’ favour) is that it echoes contemporary culture. The huge interest in, and continual theorising about, the disappearance of an infant; the castigation of detectives for their incompetence; the swings of compassion towards or against suspects — all mirror the case of our own missing child, Madeleine McCann.

“It hit me forcefully,” Summerscale says. “I had almost finished writing when Madeleine went missing. My story struck so many chords. In particular, in that the public at large forgets about the people involved being real. People begin to treat the family, who are in agony, as characters in a book or a game whom you can arrange in different configurations to come up with different scenarios.

“In both cases, the suspicion fell on the parents. There was also the great parallel that Whicher was sent from Scotland Yard when the bumbling local police had botched the job, which seemed like our attitude towards the Portuguese police.”

Summerscale is intrigued, too, by mid-Victorian attitudes to surveillance, a subject that remains at the heart of national debate. She notes in an early chapter that “there had been outrage in the early 1830s when it came to light that a plain-clothes policeman had infiltrated a political gathering”. In this environment, detectives were morally ambiguous figures. They were at once analytical geniuses delivering what the public wanted — a solution to a crime — and prurient agents of surveillance.

“I was amazed that the horror of being spied on was seen, at the time, as a national characteristic,” she says. “Privacy, especially the privacy of the home, was written about at length in newspaper editorials and books. For this reason, it was difficult to get the police force established at all, and even harder to bring in detectives. In fact, the first eight were appointed by stealth.

“Detect comes from Latin, to ‘unroof’ — literally, to lift the roof off a house and look around. That was the power and the threat of the detective. He looked into the inner sanctum of Victorian life. That transgression was particularly controversial in this case, because it was a lower-class detective looking into a middle-class family.”

The detectives, however, had access to what the public craved. And, with a hypocrisy modern readers will recognise, the newspapers voiced disgust at the intrusions made on the Kents while keeping their audience glued to every development by planting reporters at the family’s door. This was, says Summerscale, “the beginning of the mass media. There was, in particular, a huge thirst for crime reporting”.

The detective story might be a tragedy with a happy ending, but The Suspicions of Mr Whicher concludes more poignantly. Nobody connected with the case emerges with their credit intact, despite a conclusive answer to the “whodunnit” mystery. Herein lies Summerscale’s talent. In investigating a case in which the characters became pawns in a game, she restores every character in the book to a living, breathing human. Samuel Johnson would have approved.

The Suspicions of Mr Whicher is published by Bloomsbury at £14.99. To buy it for £13.49, including p&p, call The Sunday Times BooksFirst on 0870 165 8585 or visit timesonline.co.uk/booksfirst

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• The Sunday Times 100 best holiday reads
• What will we be reading this summer: the booksellers predict
• Literary festivals: a survivor’s guide