Brian Cleary, a clinical pharmacist in Dublin, was trawling through the archives at the National Library of Ireland a few years ago when he stumbled across something extraordinary: a virtually unknown short story by Bram Stoker, author of the Gothic masterpiece “Dracula.”

The story, a creepy tale of the supernatural called “Gibbet Hill,” had been published in a now-defunct Irish newspaper in 1890 but had not appeared in print or, it seemed, been mentioned anywhere since.

“I was just gobsmacked,” said Cleary, who works as the chief pharmacist at the Rotunda maternity hospital and has long been fascinated by Stoker. “I went and checked all the bibliographies, and it was nowhere. I wanted turn around and shout, ‘Guess what I found?’ but there were proper researchers and academics there, and I was just an amateur.”

Indeed, the story wasn’t included in Stoker’s archival papers and was unknown to scholars, said Audrey Whitty, director of the national library.

While it isn’t unusual for something unexpected to turn up in the library’s archives — a collection of 12 million items — Cleary’s discovery stands out for the way he made it, she said.

He first spotted a reference to “Gibbet Hill” in a promotional advertisement in the Dublin Daily Express on New Year’s Day 1891. Then he tracked down the special section in which the story had appeared — two weeks earlier, on Dec. 17, 1890 — and where it had been “hidden in plain sight,” she said.

The story takes place in Surrey, England, at a spot that became infamous when three men who had killed a sailor were hanged in the 18th century. (A gibbet is a gallows.) A young man goes for a stroll and comes upon three eerie children: a boy “with hair of spun gold” and a wriggling mass of earthworms concealed in his clothes, and two pretty, dark-haired Indian girls.

The children perform a strange ritual involving music and a snake (for starters), tie the man up and menace him with a sharp dagger.

Though he passes out and isn’t sure what happens next — they are gone when he wakes up — the unsettling experience has repercussions that do not bode well for his future.

“Gibbet Hill” is a creepy little tale. It is also, according to Paul Murray, author of the biography “From the Shadow of Dracula: A Life of Bram Stoker” and an expert on Stoker, “very significant” and “an important new addition to the canon.”

The story, and the book it will be included in, are to be unveiled to the public during Dublin’s annual Bram Stoker Festival beginning Friday. (Ireland, a supremely literary nation, commemorates many of its writers with special festivals.)

Cleary said he hoped the book would draw attention to the breadth of Stoker’s work: In addition to “Dracula,” Stoker wrote more than a dozen other novels and several short story collections, and worked for many years as the manager of the Lyceum Theater in London.

“Gibbet Hill” was published at a pivotal moment in Stoker’s career, when the author was beginning work on “Dracula.” Many of the novel’s thematic preoccupations — the thin line between normalcy and horror; the shadowy transactions between the living and the dead; the elements of Gothic weirdness — show up in the story.

And in common with “Dracula,” Stoker presents the events of “Gibbet Hill” so naturally that he makes “the incredible seem credible,” Murray said. “It’s a story you can’t explain rationally, and yet it’s so well presented that it carries you along.”

Finally, it has a theme of colonial unease also expressed in other books from that era, like Wilkie Collins’ “The Moonstone,” published some 20 years earlier: “the English fear of the threat coming from the periphery of the empire to exert revenge and disrupt English life,” Murray said. “It’s the idea that there would be this invasion of foreigners into England.”