In the summer of 1889, the managing editor of the American magazine Lippincott's visited London to commission new fiction from some up-and-coming authors. On 30 August, he held a dinner at the Langham hotel attended by Oscar Wilde and Arthur Conan Doyle, among others. The upshot was an unprecedented and remarkable double: Dorian Gray and a new Sherlock Holmes novel, originally titled The Sign of the Four.

The influence of The Moonstone (No 19 in this series) is unmistakable from the moment Holmes's client, Mary Morstan, presents herself in Baker Street. Her father, an Indian army captain, has gone missing. As a second puzzle, she reports that over the last several years, on 7 July, she has received six pearls in the mail from an unknown source. Mary Morstan can offer the great detective only one clue, a map of a fort found in her father's desk, with the names of three Sikhs, and a certain Jonathan Small. It is, of course, enough.

The story that Holmes swiftly unravels will involve some potent aspects of India in all its mystery and romance: the "mutiny" of 1857; stolen jewels from Agra; and a Sikh plot. On only his second outing in a full-length novel, Holmes is on top form throughout, stimulated by injections of cocaine and his celebrated deductive method ("How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?") Here, unmistakably, is the voice of the master.

Conan Doyle had stumbled on the idea of the brilliant detective and his stolid sidekick (a variation on a theme best known to literature in a double act like Don Quixote and Sancho Panza) in A Study in Scarlet (1888). In The Sign of Four he deepens the Holmes-Watson relationship and has the good doctor (also the narrator) fall in love with Mary Morstan ("A wondrous subtle thing is love," declares Watson). They will eventually get married.

As a novel about a crime, The Sign of Four is inferior to The Moonstone, though superbly constructed and compelling, complete with poison darts, a disputed legacy, and an exciting chase down the Thames. It also marks the reappearance of the "Baker Street Irregulars" and an important step in the evolution of Holmes and Watson, the most successful and popular literary duo in Victorian magazine fiction.

Doyle was a keen cricketer who used to play with other writers, including the young PG Wodehouse. They became friends and Wodehuse eventually paid homage to his mentor when he created English literature's supreme double act in his Jeeves and Wooster stories.

A note on the text

In his memoirs, Conan Doyle describes how he was commissioned to write this story over a dinner at the Langham hotel with Joseph M Stoddart, managing editor of Lippincott's on 30 August 1889. Stoddart's first idea was to produce an English version of his magazine with local, British contributors. In the end, only Doyle, with typical professionalism and efficiency, delivered his copy on time for its British publication in February 1890. On its first magazine appearance, the novel was titled The Sign of the Four, following the description of the fatal symbol of murder in the text of the story. Thereafter, during several second serialisations in a variety of regional journals, the novel became known as The Sign of Four.

Eventually, Conan Doyle's second Sherlock Holmes novel would appear in volume form in October 1890 from the publisher Spencer Blackett, again with the title The Sign of Four. Later editions have varied between the two versions of the title, with most editions adopting the four-word form. The actual text in the novel nearly always uses "the Sign of the Four" (the five-word phrase) to describe the symbol in the story.

Like its prequel, A Study in Scarlet, published in 1888, The Sign of th e Four was not an overnight success. It was Conan Doyle's Sherlock Holmes stories, published in the Strand magazine after 1890 that made Sherlock Holmes a literary immortal.

Three more from Sir Arthur Conan Doyle

The Adventures of Sherlock Holmes (1892); The Hound of the Baskervilles (1902); The Case-Book of Sherlock Holmes (1927).