Was Conan Doyle a killer and a thief?

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Now the enduring maxim of that most cerebral of detectives Sherlock Holmes is being put to the test.

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Now the enduring maxim of that most cerebral of detectives Sherlock Holmes is being put to the test.

It is a mystery as dark as any of those for which his creator Sir Arthur Conan Doyle is so justly celebrated - or is he? For Scotland Yard detectives are to investigate the death, almost a century ago, of a close acquaintance of the writer - and the man accused of murder is Conan Doyle himself.

And the motive? According to the research, he stole the work, The Hound of the Baskervilles - and then poisoned the true author to cover up the plagiarism.

If that were not devastating enough, it is also being claimed that Conan Doyle did not act alone in killing his friend Bertram Fletcher Robinson, but colluded with Robinson's wife Gladys, with whom he was having a passionate affair. The accusation is in a 446-page manuscript entitled The House of the Baskervilles, completed after 11 years of investigation.

It has prompted furious counter accusations from the Sherlock Holmes Society which, appalled by the slur on Conan Doyle's reputation, has dismissed the allegations as "absolute nonsense".

But Rodger Garrick-Steele, a former psychologist, who has come up with the startling theory, based on letters, research into wills and death certificates and a certain amount of circumstantial evidence, has aroused the interest of Scotland Yard, so often the beneficiary of Holmes' sleuthing genius.

A senior crime squad detective has written to Mr Garrick-Steele promising to investigate the astonishing accusations he is making. At the core of his theory, he claims that The Hound of the Baskervilles was actually written by Bertram Robinson, a journalist who died mysteriously at the age of 36.

Mr Garrick-Steele's own detective work began in 1989 when he moved into Park Hill House in the Devon village of Ipplepen on the edge of Dartmoor, the setting for The Hound of the Baskervilles.

It is widely acknowledged that Conan Doyle's inspiration for the book, first published in instalments in 1901, came from his staying with his friend Robinson and from the tales he told of ghostly beasts on the moor. He even borrowed the name of Robinson's coachman and gardener, Harry Baskerville, to give the book itstitle.

Mr Garrick-Steele began his sleuthing when a photograph taken in 1865 of Conan Doyle as a boy, which he had nailed to the wall of the living room, repeatedly jumped from its hook. He took these ghostly goings-on as a sign to start his inquiries. It has led him to conclude that the genesis of The Hound of the Baskervilles lies in a book that written by Robinson a year earlier, in 1900, entitled An Adventure on Dartmoor. Mr Garrick-Steele has unearthed that book, claiming the similarities with Conan Doyle's work are remarkable.

"This was extremely galling for Robinson whose name is hardly on the book" - it is in the acknowledgments - "while his gardener, Harry Baskerville, rode supreme on the cover in gold leaf."

The book was a huge success, coming eight years after Conan Doyle had killed off the beloved detective by having him plunge over the Reichenbach Falls in pursuit of his arch-enemy, the evil genius Professor Moriarty. The resurrection of Holmes was a publishing masterstroke but, according to Mr Garrick-Steele, it was only possible thanks to Robinson - and that put Conan Doyle in a "very ignominious position", he says.

"Doyle could now see a great big threat and had a tremendous motive for getting rid of Robinson. In fact, Doyle had to get rid of Robinson."

According to Mr Garrick-Steele, Gladys Robinson, frustrated at her inability to have children with her husband, then began an affair with Conan Doyle. "Using his extensive medical knowledge - remember Conan Doyle trained as a doctor and Holmes is famous for his knowledge of poisons - he persuaded Gladys to administer gradual, but lethal doses of laudanum to her husband."

Robinson died aged 36 on January 21, 1907, officially of typhoid and was buried at Ipplepen. Mr Garrick-Steele believes exhumation of the body will show he died from poisoning. He is lobbying the Home Office for permission to dig up the remains. "A lot doesn't add up - such as a photograph of a very healthy looking Robinson taken in the month of January when he was supposed to be on his death bed.

"I have put together a jigsaw although there are still one or two pieces missing. But it all points to a horrifying picture of a cover-up. "

The Sherlock Holmes Society is not taking the allegations lying down. "The whole thing is a complete fabrication. The origin of the idea came from Fletcher Robinson but there is no doubt the book is by Conan Doyle," said a spokeswoman for the society, barely containing her disgust.

Conan Doyle died in 1930 having spent the latter part of life dedicated to spiritualism. His death was followed by a mass seance at the Royal Albert Hall but despite the crowd's urgings, he failed to materialise. If only he could speak up, perhaps we would learn who really wrote The Hound of the Baskervilles.