‘The Illustrious Client’ could be exposed in new Sherlock Holmes exhibit

The last mystery of Sherlock Holmes will perhaps be uncovered when the manuscript of The Adventure of the Illustrious Client is exposed next month in a major Sir Arthur Conan Doyle exhibition at the Museum of London.

For Holmes's myriad fans and fan clubs around the world, the document would help decide whether the Austrian baron Adelbert Gruner was a murderer as well as a philanderer, as Holmes suspects but refuses to confirm ''in the absence of sufficient data''.

The manuscript was bequeathed to the Scottish nation in the will of Sir Arthur's daughter; but it has been held back in a vault at Coutts Bank in London, out of public view, for many years while museums in Scotland vied for the honour of displaying it.

The true identity of the "illustrious client" of the title, the man who comes to ask Dr Watson for discreet help, is famously never revealed to the reader in the story. Now devoted Holmes-ians will be able to search for clues laid out in Conan Doyle's own handwriting.

After the author's death in 1930, the manuscript was inherited by his daughter, Dame Jean Conan Doyle (Lady Bromet, as she would then be called). She died in 1997. One of the terms of her will was that a Holmes manuscript from her collection should be chosen by her executor and given to, in her lawyer's words, "a museum in Edinburgh".

The manuscript has been loaned by its latest owner, the National Library of Scotland, in a key contribution to an exhibition that claims to be the most comprehensive since the Festival of Britain paid tribute to Doyle's creation in 1951.

Sir Arthur studied medicine in Edinburgh. In later life he virtually confirmed that the enduring character of Sherlock Holmes was based on his chemistry lecturer Dr Joseph Bell, whose powers of observation and deduction rivalled those of Sherlock or his brother Mycroft Holmes.

"The links between the author and Edinburgh are well-known and long-established," said Robin Smith, head of collections and interpretation at the National Library, this weekend, explaining the decision to loan the precious manuscript. "We hope that many people will visit the Museum of London to learn more about one of the world's greatest fictional creations."

Written in 1924 and published in 1927, the last Sherlock Holmes story tells how the sleuth saved a young Englishwoman from a potentially deadly marriage. It appeared in the last Holmes compilation, containing 12 short stories, entitled The Case-Book of Sherlock Holmes.

The curator of the new Sherlock Holmes exhibition, Alex Werner, said, The Illustrious Client story is important as it plays to one of the central themes of the exhibition – that Sherlock Holmes is immortal and all attempts to kill him fail. The manuscript reveals a violent attempt to kill Sherlock Holmes. Dr Watson learns of the 'murderous attack' from a newspaper placard near Charing Cross station."

Conan Doyle of course wrote a great deal apart from his Holmes stories – his historical fiction (The White Company, Sir Nigel, Micah Clarke) were regarded highly by Winston Churchill, and would be eminently filmable today.

But critics as well as readers agree that creating a character of the magnitude of Sherlock Holmes is what secures Sir Arthur's place in the literary pantheon.