Step into any bookshop, whether it's that flashy new one on the high street or the little-used paperback exchange in a run-down part of town, and you will almost certainly find - in the fiction or mystery section - some edition of The Adventures of Sherlock Holmes. For well over 100 years, the great sleuth of Baker Street has been a staple of our imagination, known the world over for his Inverness cape, calabash pipe and deerstalker cap. He is quite probably the most famous, most immediately recognisable fictional character ever created.
Eccentric aesthete, expert chemist and linguist, master of disguise, amateur boxer and baritsu adept, occasional philosopher and overall polymath, Holmes lives by his wits and entirely for the practice of his art - "the art of detection". He is, according to the biographer Hesketh Pearson, "what every man desires to be", nothing less than a "knight errant who rescues the unfortunate and fights single-handed against the powers of darkness".
At his side is his faithful companion and chronicler, Dr John H Watson. In the old Basil Rathbone films, Nigel Bruce portrayed Watson as a bumbling idiot, but more recently actors such as Edward Hardwicke, Jude Law and Martin Freeman have shown that he is, in his own way, as admirable as his better-known friend. A soldier and doctor, susceptible to feminine beauty, a devoted husband to at least two wives, he is both Holmes's straight man and a partial self-portrait of the author. Over the 56 stories and four novels, we see the great thinking machine gradually humanised, to some extent, by the kindly Watson.
Agatha Christie's Hercule Poirot once spoke of The Adventures of Sherlock Holmes, then reverently murmured the single word: "Maître." Was the Belgian detective referring to Holmes?
Ah, non, non, not Sherlock Holmes! It is the author, Sir Arthur Conan Doyle, that I salute. These tales of Sherlock Holmes are in reality far-fetched . . . But the art of writing - ah, that is entirely different. The pleasure of the language, the creation above all of that magnificent character, Dr Watson. Ah, that was indeed a triumph.
Christie is just one of many writers who have recognised and honoured Conan Doyle's artistry. John le Carré has pointed to the "narrative perfection" of the Holmes stories, emphasising, like Dorothy L Sayers before him, their subtle "interplay between dialogue and description", their "perfect characterisation and perfect timing". Peter Ackroyd has spoken of the "melancholy intensity and majestic cadence" of Conan Doyle's prose, "striated with rich local detail, so that he seems effortlessly able to evoke the marvellous and the terrible in the ordinary". Distinguished novelists as various as Eric Ambler, Angus Wilson and P G Wodehouse have been proud to introduce new editions of the tales of Baker Street. Indeed, Wodehouse is arguably Conan Doyle's greatest disciple, creating in Jeeves and Wooster comic versions of Holmes and Watson.
All too often, posterity remembers some authors, no matter how multifaceted their genius, for only one or two books. Who, aside from scholars of Victorian fiction, now reads anything by Thackeray other than Vanity Fair? Jane Eyre has largely driven out Charlotte Brontë's great depiction of loneliness, Villette. From early on, the worldwide popularity of Holmes annoyed his creator, and with cause: the detective's adventures, wonderful as they are, tended to overshadow everything else Conan Doyle wrote, with the partial exception of The Lost World, his 1912 adventure novel about the discovery of living dinosaurs on a South American plateau.
In my new book, On Conan Doyle, I try to redress this imbalance. I discuss the Professor Challenger science-fiction stories, the dozens
of supernatural tales and contes cruels and the historical fiction, especially The White Company (which is often derided these days) and the rousing Brigadier Gerard swashbucklers, an important influence on George MacDonald Fraser's Flashman novels.
There are sections covering Conan Doyle's lively essays, memoirs and non-fiction - he wrote frequently for the newspapers about divorce law reform and miscarriages of justice – and an overview of his novels about contemporary life. These show him addressing such social and political themes as religious doubt, women's rights and even Middle East terrorism. Nearly everything that Conan Doyle wrote is astonishingly readable and often quite funny. I close with a brief consideration of the writer's last years, when he devoted himself to spiritualism.
I also include a couple of chapters about the Baker Street Irregulars, the American sodality that was founded in the 1930s to honour Holmes. In the UK, the equivalent group is the Sherlock Holmes Society of London. Both organisations play what has been called "the grand game", in which the Holmes canon is treated as historical fact, rather than fancy, and the tools of criticism and textual scholarship are used to harmonise the various inconsistencies in the canon or to speculate about some of its lacunae.
In Britain, for instance, there has been a decades-long debate about whether Holmes attended Oxford or Cambridge as a student. (Christopher Morley, a native of Baltimore and founder of the Baker Street Irregulars, thought the future detective might have done graduate work at Johns Hopkins.) Sayers always insisted that the game should be played with an absolutely straight face.
In the stories, Watson often refers to certain cases for which the world is not yet prepared, the most celebrated being that of the "giant rat of Sumatra". In so doing, he tacitly suggests the possibility of an unending number of Sherlockian adventures; hence the hundreds of parodies and pastiches of the past century.
Ever since Nicholas Meyer brought out The Seven-Per-Cent Solution in 1974, there has been a spate of such works of homage and revisionism. John Gardner gave us three novels about a rather admirable Professor Moriarty. Arthur and George, the 2005 novel by this year's winner of the Man Booker Prize, Julian Barnes, is adapted from an episode in Conan Doyle's life in which he came to the rescue of a young lawyer who had been wrongly accused of bizarre crimes.
More recently, John O'Connell, in The Baskerville Legacy, imagined that Conan Doyle's friend Bertram Fletcher Robinson did more than suggest the plot for that "real creeper", The Hound of the Baskervilles. This autumn, one can also read The Narrative of John Smith, Conan Doyle's incomplete first novel, now edited with annotations by two authorities on his life, Jon Lellenberg and Daniel Stashower, assisted by the British Library curator Rachel Foss.
Anthony Horowitz's The House of Silk, another new Holmes novel, is almost certain to be an international bestseller. In Pirate King - the latest in a series that began with The Beekeeper's Apprentice (1994) - Laurie R King continues the adventures of Holmes with his partner (and wife!), Mary Russell. There is even a new collection of stories, A Study in Sherlock, edited by King and Leslie S Klinger and featuring fresh Baker Street exploits by authors such as Lee Child, Neil Gaiman and Jacqueline Winspear.
Though the great detective may be irrevocably associated with the gaslights and hansom cabs of 1895, clearly Holmes is as endlessly appealing and adaptable as that most Sherlockian of Shakespeare's characters, Hamlet. Just look at the moody, Heathcliff-like, text-messaging heart-throb portrayed by Benedict Cumberbatch in the BBC's Sherlock or the gritty, steam-punk action hero played by Robert Downey Jr in Sherlock Holmes and its upcoming sequel.
Still, in the end, we always go back to the original stories and to those cluttered rooms in Baker Street from which Holmes and Watson sally forth to do battle on gloomy Dartmoor or in "the lowest and vilest alleys" of the great metropolis. Does anyone ever forget the insidious threat found in five orange pips, the fearful cipher of "the dancing men", or the hideous death inflicted by "the devil's foot"? Who does not shudder at the memory of the cobra-like Moriarty?
As long as there are readers, people will be thrilling to Holmes's immortal promise: "Come, Watson, come! The game is afoot!" Still, it is good to remember that his creator wrote much else worth reading besides the tales of Baker Street. In the words of Herbert Greenhough Smith, editor of the Strand magazine, Conan Doyle was nothing less than "the greatest natural-born storyteller of the age".
Michael Dirda is a Pulitzer Prize-winning literary journalist and the author of "On Conan Doyle" (Princeton University Press, £13.95)