A cult-film holy grail had, purportedly, been unearthed last week: a scrapped 2009-era script for a third Ghostbusters movie, leaked to the website Bloody-Disgusting.com.

It quickly shot around the Internet, and fan sites piled on: "It could have been awesome," wrote JoBlo.com. "I really like the overall sound of this," said ScienceFiction.com. On social media, fans were less restrained, if more polarized: "My God that would've been amazing," wrote one of hundreds of commenters, while another said it "sounds like shit."

The script's alleged backstory followed the established Ghostbusters 3 narrative: a passing-of-the-torch tale penned by The Office writers Lee Eisenberg and Gene Stupnitsky that fizzled from the spotlight as franchise co-creator Harold Ramis fell ill. After Ramis's death earlier this year, the film switched directions, with Bridesmaids director Paul Feig tapped to direct and co-write an all-female reboot.

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Eisenberg and Stupnitsky, though, had nothing to do with this script. It was written by Sean Grady, a 28-year-old Halifax filmmaker with an absurd sense of humour.

"The Internet," he says, "is such a beautiful place."

When Grady anonymously submitted the script last Monday – on a whim, with Eisenberg and Stupnitsky's names stamped on it to look official – it was as a casual prank, designed to get honest feedback on his writing and ideas. But the leak quickly spiralled out of control, as site after site began posting, summarizing and discussing the script without actually verifying it. Soon, the news would be aggregated onto IMDb and discussed at length on Reddit.

Grady calls it a "vindication" of his writing. "The amount of criticism it's gotten is very educational to somebody that wants to write," he says. "It felt very good that the story I thought would work was so positively received by a lot of people."

The script was the product of three years of boredom. In downtime during day jobs – usually editing film, but also during a stint as a gas-station attendant – Grady slowly put together a fake script for a third Ghostbusters film to pass the time.

The New Brunswick-born filmmaker gets a lot of writing done this way. Monster Island, a short horror film he wrote at the same time, aired at the Toronto After Dark Film Festival last month.

Getting feedback on his own scripts has long proved difficult; Halifax is a film-friendly city, but the industry there is neither big nor fast-moving. Earlier this year, Grady started reaching out to industry types for comment with a fair amount of success. He got brief comments from various producers and screenwriters, including Michael C. Gross, a producer on both original Ghostbusters films, who called Monster Island a "work of art" both "wonderfully" directed and written.

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Last week, after reading about fake Batman reboot scripts that floated around a decade ago, Grady realized a way to get far more feedback. He tidied up his Ghostbusters script, which he hadn't touched for a year, and leaked it from a fake e-mail address.

The original two films were written by Ramis and Dan Aykroyd. In Grady's treatment, titled Ghostbusters, Inc., their characters Egon Spengler and Ray Stantz have been ousted from their own company after it went public; meanwhile, Bill Murray's Peter Venkman abandoned his friends in a successful bid to become New York's mayor. Grady conceived the plot to mirror Murray's real-life falling out with Ramis.

After a Slender Man-like villain escalates his attacks across New York, Venkman is forced to reunite with his ghost-busting pals, only to die with them in battle as their proton streams cross paths. But Ghostbusters, Inc. lives on, with Winston Zeddemore (Ernie Hudson) and Venkman's son Oscar heading the company, as the film ends with the core trio playing cards – now, appropriately, as ghosts themselves.

As websites picked up on the Bloody-Disgusting.com story, a pattern emerged – no one was verifying if the script was authentic. A lone Ghostbusters fan site eventually put the question to Stupnitsky on Twitter, where he finally outed it as a fake.

Feeling bad about misrepresenting the writers, Grady reached out to Bloody-Disgusting to apologize; the site has since updated their story to refer to him as a nameless "desperate writer."

Not that Grady's deterred by that. "It was an amazing response for a lowly, desperate writer."