"The Mystery of the Worm" by John Pelan (from Shadows Over Baker Street, edited by Michsel Reaves & John Pelan, 2003; reprinted in Pelan's collection Darkness, My Old Friend, 2016)
In "The Problem of Thor Bridge," Watson mentions an unpublished case of Sherlock Holmes -- "a remarkable worm said to be unknown to science." Watson's notes on the case remained locked in a safe deposit box until mankind was ready to hear of this amazing adventure. Thirty years later, Holmes was cultivating bees in retirement in Suffolk and Watson finally revised the notes into a full record; still, mankind was not ready, so the full story once again went into a secure location.
The time is 1894, a few months after Holmes dealt with "the ferocious Colonel Moran." A man claiming to be Dr. Robert Beech appeared at Holmes' lodgings, asking his help to translate marking on an indecipherable cylinder. The cylinder, about a foot long and four inches wide and made of some greenish metal, was covered with "a chaotic melange of whorls, slashes, and geometric shapes." Beech also produced a crudely carved star-shaped stone =and a glass vial containing a "singularly repulsive floating in formaldehyde. The worm had nasty looking mandibles surrounding what appeared to be a stinger. The items were recovered from a lost city in the Egyptian desert.
Holmes told his visitor to leave, calling him no more than a common fraud. The man quietly left, leaving Holmes to explain his reasoning to Watson. Shortly thereafter, the man who had sent "Beech" to Holmes appeared. He was Doctor Nikola, the evil protagonist of a series of five fantastic novels (1895-1901) by Australian writer Guy Boothby. Nikola told Holmes that he had passed Nikola's test by identifying "Beech" (who was really Nikola's assistant Persano); Holmes thus proving to have a great intellect -- almost as great as Nikola's own.
Nikola, who appeared to be about 35 years old, claimed to be much older due to his scientific researches. Nikola's goal was to achieve immortality. He had hoped to gain the secret from "a Chinese gentleman who I have every reason to believe was young when the pyramids of Giza were being constructed;" but that relationship fell through, but not before Nikola had sampled a certain compound the Chinese gentleman had developed. (The Chinese gentleman, unnamed, would later launch an attack of England. Guess who?) Nikola believed there were others who possessed this Elixir Vitae and that they could be persuaded to share its secret with him. These "others" were not of this Earth. In his researches, Nikola learned of a lost city buried in the Egyptian sands which may hold the secret of the magical elixir.
Nicola located the city and found a series of massive column, each with a star-shaped stone bolted to the top. As a matter of habit, Nikola's tent was located far from his bearers and the columns. During the night, one bearer attempted to steal the star stone. The next morning the entire camp was empty, with only red blood seeping into the sand. The star stone was located just a few feet from its column. Nikola reasoned that whatever beings came that night had been previously prevented from reaching this world by the proximity of the star stone to the columns. Now he is ready to call these beings by placing the star stone away from its column. And he wanted Holmes' assistance.
Holmes and Watson find themselves in dire danger after realizing that this was merely one of Nikola's experiments...
And the worm? It turns out that this was just one of several species left behind by the beings from whatever dimension they came from.
Not germane to the story itself, but it is interesting that Watson mentions two of his writer friends in this story: Dick Donovan (real name James Edward Preston Muddock, the prolific author of mystery and horror stories, whose tales were as popular at the time as those of Conan Doyle, and "Burke", presumably Thomas Burke, who wrote popular stories about the Limehouse area of London.
John Pelan (1957-2021) was a knowledgeable author, editor, and publisher of small-press science fiction and weird and horror fiction. He was the recipient of the International Horror Guild Award and the Stoker Award.
