An author who gave up her job to investigate and write about a notorious unsolved murder that happened in 1860 has won the richest prize in nonfiction.

The Suspicions of Mr Whicher: or the Murder at Road Hill House by Kate Summerscale was awarded the £30,000 BBC Four Samuel Johnson Prize at the Royal Festival Hall last night. Summerscale beat the favourite, The World is What It Is: The Authorised Biography of V. S. Naipaul, Patrick French’s unflattering portrait of the Nobel laureate.

The Suspicions of Mr Whicher is a whodunnit based on the killing of Francis Saville Kent, the three-year old son of an apparently respectable factory inspector at the family’s Georgian country house. The boy was stabbed in the chest and had his throat slashed. His body was found in a privy.

With jealous half-siblings, a dead mother who had gone mad, a cruel governess turned stepmother and a staff of gardeners, stable-hands and servants in the mix, the crime scandalised Victorian society.

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: The Road child murder

• Case of Constance Kent

• Constance Kent indicted

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Theories about the killing were thrashed out at dinner parties and the murder fuelled the 1860s phenomenon of the “sensation” novel, inspiring Wilkie Collins’s The Moonstone among others. Thirty years later the cult of the detective peaked with the creation of Sherlock Holmes.

Detective Inspector Jack Whicher, one of the original eight Scotland Yard detectives, was put in charge and concluded that the murder was an inside job. Whicher was 45, shabby and grizzled and the country went wild for him, although ultimately the case left him a broken man.

Summerscale wrote: “A Victorian detective was a secular substitute for a prophet or a priest. In a newly uncertain world, he offered science, conviction, stories that could organise chaos.”

She stumbled on the story in an 1890s anthology of unsolved crime stories and became so fascinated that she left her post as literary editor of The Daily Telegraph to pursue her investigations. She spent a year researching the book and another year writing it.

Summerscale said that she borrowed devices from detective fiction to lend suspense to her meticulously sourced reconstruction: “I was trying to make it as close to a classic detective novel as possible. It was tricky because I was writing about the form and in the form at the same time.”

Last night, after winning the award, she said: “It did feel strange sometimes to be so involved in something so terrible and dark, no matter how long ago it was. You can forget the emotional reality. When I remembered, it would give me a great jolt.” She added that she was “very happy” to have beaten the bookies’ favourite.

Rosie Boycott, chairwoman of the judges, said that the book was “a dramatic page-turning detective yarn of a real-life murder that inspired the birth of modern detective fiction. Kate Summerscale has brilliantly merged scrupulous archival research with vivid storytelling that reads with the pace of a Victorian thriller.” The book, Summerscale’s second, is a hardback bestseller.

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