It is a truth universally acknowledged that a Jane Austen novel in possession of added gore will be a surefire best-seller.
That's the conclusion reached by publishers since the success of Pride and Prejudice and Zombies, an unlikely literary sensation created by adding dollops of "ultraviolent zombie mayhem" to Austen's classic love story.
Zombies - billed as 85 percent Austen's original text and 15 percent brand-new blood and guts - has become a best-seller since it was published earlier this year, with 750,000 copies in print. There's a movie in the works. And it has spawned a monster - or, more accurately, a slew of literary monster mash-ups.
Next month, Zombies publisher Quirk Books is releasing Sense and Sensibility and Sea Monsters, which adds giant lobsters and rampaging octopi to Austen's love story.
Out this week from another publisher is Mr. Darcy, Vampyre, a supernatural sequel which portrays the aloof hero of Pride and Prejudice as an undead bloodsucker. Later this year comes Jane Bites Back, in which the author herself develops a taste for blood.
Even Austen purists admit a grudging admiration for the Zombies concept.
"In publishing terms, it's brilliant," said Claire Harman, a Columbia University professor and author of Jane's Fame: How Jane Austen Conquered the World.
"Why did I spend three years writing a critical book on Austen? Why didn't I just think of that?"
Quirk Books editorial director Jason Rekulak said he was inspired by the internet-unleashed wave of "creative copyright infringement" - musical and video mash-ups that mangle styles and genres for comic or dramatic effect.
He made a list of classic books whose copyrights have lapsed and were ripe for pillage, from Moby Dick to Great Expectations.
"Then I made a list of things that might enhance these novels - robots, ninjas, zombies," Rekulak said. "As soon as I drew a line between 'Pride and Prejudice' and zombies, I knew I had a great title."
The irresistible title is key to the success of Pride and Prejudice and Zombies. The book itself keeps most of Austen's story - girl meets boy, girl hates boy, girl is won over by boy's good looks and large fortune - with added chunks of zombie violence by US writer Seth Grahame-Smith.
Zombies and its successors are the latest mutant offshoots of the unstoppable Austen industry.
The author wrote just six novels before she died at age 41 in 1817, but they have inspired endless spinoffs, from "chick-lit" novels like The Jane Austen Book Club to time-travelling TV series Lost in Austen and Bollywood-tinged movie Bride and Prejudice.
There are books on everything from etiquette (Jane Austen's Guide to Good Manners) to gardening (In the Garden with Jane Austen), and a huge internet-based community of passionate Jane-philes.
It's a remarkable turnaround for a writer who achieved limited success in her lifetime and was largely forgotten after she died.
Harman, who studied Austen's resurrection by a band of late 19th-Century admirers, said her global fame rests partly on the appeal of her elegant, witty books, with their blend of social commentary, feisty heroines and romantic happy endings.
"Because there are only six of them, (readers) want more and they will riff on the scenes she provided," Harman said. "People want to wallow. They want to get in that lovely warm bath and have a longer bath."
And partly, Harman said, it's good timing, "a kind of technological luck."
The emergence of the internet coincided with a wave of Austen adaptations, including the BBC's 1995 Pride and Prejudice and Ang Lee's adaptation of Sense and Sensibility the same year, that brought the writer new fans.
That doesn't explain the surprising affinity between Austen's Regency world, with its horse-drawn carriages, country-house balls and empire line dresses, and the supernatural.
"There's more overlap between the two worlds than I ever imagined," said Rekulak, who was startled to find a large number of Austen fans at Comic-Con, the San Diego conference devoted to all things science fiction and fantasy.
"It struck me that that kind of Regency romance is its own sort of fantasy," he said.
It's not so far-fetched to see echoes of handsome, brooding Mr. Darcy in the teen-heartthrob vampires of the Twilight books and movies or the TV series True Blood.
Amanda Grange, author of Sourcebooks' Mr Darcy, Vampyre, said she found it easy to add dark, Gothic overtones to the story of Darcy and Lizzy Bennet. Austen wrote against the backdrop of the Napoleonic wars, and in an era that produced Mary Shelley's Frankenstein and the first vampire stories.
Like many good publishing ideas, the trend could soon spiral out of control. Rekulak says he can't stop friends and family sending him ideas for more books - he has a list of more than 200 titles, from A Farewell to Arms and Legs to The Brothers Kara-zombie.
The coming months promise more in the same bloody vein from a variety of publishers, including Queen Victoria: Demon-Hunter and I am Scrooge: A Zombie Story for Christmas.
In the United States, where Quirk Books is based, all books copyrighted before 1923 are in the public domain. For other books, copyright generally expires some decades after the author's death, but this varies from country to country.
If nothing else, the trend proves the willingness of readers and writers to eliminate the gap between pop culture and what used to be known as high art.
Grange said she had the idea for her story years ago while watching Buffy the Vampire Slayer, the TV show about a suburban California student who battles demons.
"I just thought that if they ever did a Pride and Prejudice episode it would work really well," Grange said. "You could have Buffy as Lizzy and Angel as Darcy.
"People used to live in more compartmentalised worlds," she said. "Now we are exposed to all of it - we study the classics at school but then we go home and watch TV."