The biggest thorn in Sir Arthur Conan Doyle’s side was the world’s obstinate obsession with just one of his creations: Sherlock Holmes. And now, 94 years after the author’s death, the story is much the same: the deerstalker hat and pipe remain the internationally recognised emblems of the greatest detective who never lived. The boxing gear of Rodney Stone, his other adventuring hero? Or the bushy beard of The Lost World explorer Professor George Challenger? Not so much.

But Conan Doyle’s descendants have a longterm plan to correct this imbalance, and the Observer can reveal their latest weapon. Thriller writer Gareth Rubin is bringing out a new, officially approved Holmes story that will give equal billing to arch-villain Professor James Moriarty. The new novel unites the detecting skills of the talented sleuth with those of his greatest adversary, a criminal mastermind who runs an unseen network of thieves, murderers and blackmailers and yet never leaves a trace to link him to the scene.

“One of our aims is to get the world to know more about other Conan Doyle characters. And not just Moriarty, but those in other Holmes mysteries, like Colonel Sebastian Moran, or in other adventure series, like the Professor Challenger stories,” said Richard Pooley, Conan Doyle’s step-great-grandson and the man who runs the literary estate alongside Doyle’s great-nephew, Richard Doyle, and his great-niece, Catherine Bates. The family have endorsed Rubin’s book, Holmes and Moriarty, as a worthy successor. “Gareth has drawn these characters very well, including Colonel Moran, who is key to this story,” added Pooley. “Moran was once described by Holmes as ‘the second most dangerous man in London’, and he tells half of this new mystery. As Moriarty’s right-hand man, he only crops up in a couple of original Holmes stories, I believe.”

Efforts to spin out fresh entertainment from an established piece of work have become crucial to profitably managing a literary property. Earlier this month, the Roald Dahl Estate announced new books about his most popular characters, each penned by different authors, including Greg James, Konnie Huq and Adam Kay.

In the same way, the owners of Agatha Christie’s back catalogue, a company now run by her great-grandson James Prichard, have looked to relaunch her vast output of work in new ways. Mystery writer Sophie Hannah has been in charge of revitalising Hercule Poirot in print, while on television the screenwriter Sarah Phelps added some edgy terror to Christie’s screen adaptations, and Sian Ejiwunmi-Le Berre gave an equally controversial, anti-colonial rendering of Murder is Easy last Christmas.

The idea of forging a link between Holmes and Rubin, a Londoner who works at the Observer and is best known for his recent bestseller The Turnglass, came from Rubin’s agent, Jon Wood. More than a decade ago, it was Wood who suggested that Anthony Horowitz should write earlier authorised Holmes titles, The House of Silk, in 2011, and its 2014 follow-up. Since these books, only film and theatre scripts about Holmes have been officially sanctioned by the family as sequels.

“Gareth has really developed the personas and is so good at dialogue,” said Pooley, who suspects that Moran, “a young guy”, could now spawn his own series. But there is potential too, he believes, in Professor Challenger, as well as in the boxer, Stone.

Also significant in the Holmes mythology, of course, are Sherlock’s reclusive brother Mycroft and the villainous Irene Adler, the only opponent to get the better of Holmes and one subsequently always referred to as “the woman”.

“We’re already talking to people who want to take Irene on to develop a television series. Most of Conan Doyle’s recurring characters were men, although the stories are often about women in peril. All that comes from his character. The most important people in his life were his mother and his second wife,” said Pooley. “His own father was useless and an alcoholic, and so all his tales are about chivalry. Sherlock and Dr Watson are always saving women.”

• This article was amended on 26 April 2024 to remove a reference to Rodney Stone’s “boxing gloves”, owing to the fact that the titular Conan Doyle character was a bare-knuckle fighter.