CNN  — 

One summer evening in 1889, Arthur Conan Doyle and Oscar Wilde sat down for dinner at the Langham Hotel in London with J.M Stoddart, the American businessman and editor of Lippincott’s Monthly Magazine.

By the time they left, Wilde had committed to writing “The Picture of Dorian Gray” and Conan Doyle had agreed to write “The Sign of Four,” one of his most famous Sherlock Holmes stories.

Now, Conan Doyle’s letters recounting that fated dinner and his sole handwritten manuscript of “The Sign of Four” are being auctioned by Sotheby’s New York, alongside other literary treasures.

The manuscript alone is expected to fetch up to $1.2 million, given its unique significance and status as the most valuable Conan Doyle item ever offered at auction, a Sotheby’s statement said.

“It’s hard to think of two contemporary authors who might be less similar than Conan Doyle and Oscar Wilde,” Selby Kiffer, the auction house’s international senior specialist for books and manuscripts, told CNN.

“And yet there they are at a dinner table together and talking about what they’re currently working on.

“So you’re put in the milieu of the time, and that really helps (us) understand the genesis and the creation of the manuscript in a way that very seldom happens.”

The "Sign of Four" was published in 1890.

The manuscript itself is exceptionally clean, bearing only Stoddart’s edits to Americanize spellings and a few crossed-out words as Conan Doyle himself tweaked his work.

All of Conan Doyle’s other surviving manuscripts, most of which reside in museums, similarly show little sign of being edited, Kiffer added.

“Whether Doyle spent a lot of time just thinking out in his mind before he put the words down… but it seems to have sprung almost fully formed, from his mind to his pen,” he said.

“The Sign of Four” was Conan Doyle’s second Sherlock Holmes novel, commissioned by Stoddart to capitalize on the popularity of the detective’s first adventure in “The Study in Scarlet.”

Lippincott’s Magazine published the story in 1890 and, once again, the adventures of Holmes and Dr. Watson proved hugely popular with readers on both sides of the Atlantic.

The manuscript is just one fraction of a collection that was assembled by Dr. Rodney P. Swantko, a Chicago-based collector, who died two years ago.

Other lots include four novels inscribed by F. Scott Fitzgerald, one of which is a copy of “The Great Gatsby” he signed from Scott and Zelda, on behalf of his wife, which is expected to fetch up to $250,000.

First edition copies of “Lolita” that its author Vladimir Nabokov addressed and sent to fellow writer Graham Greene, as well as to his wife, Vera, are also included in the sale.

The auction will be held as a live sale in New York at 10 a.m. ET on June 26.