When Karen Hall published her debut novel, “Dark Debts,” 20 years ago, it seemed like the start of a blockbuster literary career. Hall, a veteran TV writer who had worked on hits like “M*A*S*H” and “Hill Street Blues,” had the commercial storytelling chops. She spent five years working on the novel, a pulpy theological thriller about a Roman Catholic priest who becomes mixed up with demonic forces.

“Dark Debts” was an instant success when Random House published it in 1996, with a 150,000-copy print run. Paramount optioned the film rights. Fans hounded her for a sequel, and Hall’s publisher and agent urged her to write another novel to capitalize on the momentum. “I can only hope that Ms. Hall will read these reviews, and will provide her readers with another work of fiction,” a reader pleaded in a 2001 Amazon review.

She never wrote another book. Instead, Hall spent the next two decades obsessing about the flaws of “Dark Debts.”

“I never stopped thinking about it,” said Hall, 59. “I never said it aloud to anybody, but I always knew I would never write another book until I got this one right.”

Now, the story is finally getting a second life. On Tuesday, Simon & Schuster released a new edition of “Dark Debts,” and Hall has made changes — dramatic and subtle — throughout the book. She rewrote the explosive ending, which previously finished with what she felt was an emotionally false note. She added a character and dropped a significant character from the earlier version. She toned down some of the violence and gore, including a climactic plot twist in which a possessed man goes on a killing spree, and scrubbed out the profanity, at the request of her 91-year-old mother.

“I had barely been able to read it in the last 20 years, because everything I didn’t like about it made me cringe,” Hall said. “Boy, I was in love with the sound of my own voice.”

Most artists and writers have lingering regrets about their early work, but very few of them actually get a second shot. It is rare for a novelist to exhume an old story, and even more unusual for a publisher to risk rereleasing a decades-old book that has gone out of print.

Luckily for Hall, her former editor, Jonathan Karp, shared her obsession with “Dark Debts,” and her nagging feeling that the book could have been better.

“I don’t think there’s ever been another book quite like it,” said Karp, who is now the publisher of Simon & Schuster. “It was the smartest pop thriller I ever read.”

The plan to republish it came about two years ago, when Audible approached Hall about adapting the novel into an audio drama. When Hall mentioned the project to Karp, he suggested releasing an anniversary edition of the book with him at Simon & Schuster. She told him she wanted to republish it only if she could rewrite it.

Karp, who called Hall “my own personal Harper Lee,” had been waiting for another book from her for years, and immediately agreed to publish a new version.

“Karen never felt like she nailed it, and I didn’t disagree with that,” Karp said. “There are so many books as a publisher where you miss the mark a little bit, either commercially or critically, and I’ve often wondered, why wouldn’t a writer want to try it again?”

Hall got the idea for “Dark Debts” from her friend Mikal Gilmore, a writer for Rolling Stone magazine, who told her that his mother believed there was a demonic curse on the Gilmore family. (Mikal’s brother Gary was a convicted murderer who was executed in 1977 and whose story was recounted in the Norman Mailer book “The Executioner’s Song.”)

In “Dark Debts,” Hall took the premise of a demonic curse and spun it into a thriller about a Georgia family tormented by the devil. A Jesuit priest, Michael Kinney, who is in love with a woman and drifting from his faith, intervenes and attempts to save one of the surviving family members, Jack, from the demon. Father Kinney teams up with a reporter named Randa, who has fallen in love with Jack. The resulting novel was a Southern Gothic-flavored existential mystery, with thorny theological debates about good and evil blended with graphic violence and an unlikely romance.

The novel wasn’t universally celebrated. Entertainment Weekly gave it a C- and dismissed it as “blasphemous twaddle.” The Paramount film never got off the ground.

But the book changed Hall’s life in profound ways. She was raised Methodist but had always felt drawn to Catholicism, and while researching the novel and talking to priests, she decided to convert. Two years after “Dark Debts” was published, her former high school boyfriend, Chris Walker, who had first introduced her to Catholicism, contacted her through her publisher’s website to say he enjoyed the novel. They have now been married for 16 years and live in Boone, North Carolina, where they own a small independent store, Black Bear Books.

Hall tried to write a sequel, partly to appease fans but also to atone for what she felt was a flawed ending. (In the earlier version, Father Kinney leaves the priesthood to be with the woman he loves.) But she never made it past the first chapter, despite writing 25 openings.

Now satisfied with the ending of “Dark Debts,” Hall said she is finally ready to write something new.

“My problem is I have an idea that could be a novel once every 20 years,” she said.