During the summer of 1890, a 13-year-old boy stabbed his mother to death in the bed where they both slept at a terraced house in East London.

Young Robert Coombes left the body there, locked the door, and for the next 10 days, he and his conspiring 12-year-old brother, Nattie, pawned the family’s belongings to fund trips to the seaside and cricket at Lord’s.

They told neighbours their mother was visiting family and their father was away at sea – until a strange smell started emanating from the house.

Dubbed the “Plaistow Horror,” the grisly murder caught national public attention in the Victorian press.

But more than 100 years later, it was all but forgotten.

That is, until West Hampstead author Kate Summerscale chanced upon the story while looking at old newspaper clippings.

“It immediately struck me as strange and eerie,” says Summerscale.

“I was very taken by the mixture of callousness and innocence with which they had conducted themselves.

“That was the first thing that hooked me.”

She now tells the lurid tale in forensic detail in her latest non-fiction book, The Wicked Boy: The Mystery of a Victorian Child Murderer (Bloomsbury, £16.99), which she will discuss at the Proms.

Fans of her bestselling work, The Suspicions of Mr Whicher – which was adapted into a series of standalone TV detective films for ITV – will be pleased to hear that her latest book is in the same true-crime vein.

It’s a genre that has become increasingly legitimised in recent years, with the rise of Scandi-noir dramas and the watercooler Netflix documentary, Making a Murderer.

“True crime has always has been popular,” says Summerscale. “But there is a new respectability to some of the genre, with the Serial podcast and Making a Murderer.

“Traditionally, it’s been considered a bit sleazy, so now there’s a bit more gravitas – occasionally, in certain forms.”

Details about Robert and his brother were thin on the ground.

But Summerscale combines the facts she managed to unearth with layers of context to vivdly paint the scenes for the reader.

The latter half focuses on Robert’s redemptive life after serving his time in Broadmoor.

But in the earlier chapters, one area that fascinates Summerscale was how much the Victorian press made of Robert’s love of so-called “penny dreadfuls”.

These were sensational storybooks that were cursed by the public as a bad influence on children – much in the same way violent computer games are today.

“It did strike me that very often, especially when young people commit crimes, we often reach for something in popular culture that might have made them do it,” Kate says.

“Some years ago it was ‘Video Nasties;’ now more likely to be computer games.

“I found it really fascinating and instructive to be able to look at what’s almost the same debate, but at a distance.”

She doesn’t believe the penny dreadfuls caused Robert to commit the crime – “it’s absurd” – but does concede that it could have shaped his imaginative world. We may never know the true motive for the murder and Summerscale deliberately doesn’t spell it out. Unlike the locked-room mystery of Mr Whicher, The Wicked Boy is more a “why-dunnit” than a “whodunnit”.

But part of the reason may well lie in the boys’ toxic relationship with their mother; in court, Robert said he acted after she beat Nattie.

“The fact that the boys plotted the murder together tells me that for them to agree in even a half-rational way that she deserved to die meant that something very unhealthy had developed in that household,” Summerscale says.

“But it would be wrong to blame her for her own murder – that would be easy and it would be a satisfying story to say she was a monster. I only think he believed she was a monster. There was perceived mistreatment and cruelty – yet, that’s for the reader to decide.”

Kate Summerscale is in conversation with broadcaster Sue MacGregor on Sunday at 2pm at the Proms at St Jude’s.