In "Bratva," a new crime novel by Christopher Golden, a grizzled motorcycle gang vice president named Jax Teller and his loyal sidekicks Opie and Chibs take on Russian mobsters to rescue Jax’s half sister. Some 200 pages of gun battles, fistfights and mayhem follow.

Those characters will be familiar to fans of "Sons of Anarchy," a popular motorcycle gang drama on the FX network. They were lifted wholesale from the show, which recently concluded its seventh and final season.

The novel was commissioned by the show’s creator, Kurt Sutter, to keep fans engaged with the characters – and with the show’s lucrative line of clothing, jewelry, action figures and other merchandise – after the finale.

"With the show ending, how do we continue to keep the world in the consciousness of fans?" Sutter said. "It’s always a mix of art and commerce."

"Bratva" is one of the latest entries to a flourishing but often unappreciated pocket of the publishing world: tie-in novels. Writers have produced novels based on the terrorism drama "Homeland," the British crime series "Broadchurch," and J.J. Abrams’ sci-fi series "Fringe," and more titles are coming soon.

Novels are also providing life support for characters from popular, long defunct series, like "Veronica Mars," "Buffy the Vampire Slayer" and "Murder, She Wrote." (The 43rd and 44th "Murder, She Wrote" novels will come out this year, almost 20 years after the series went off the air.)

Studios and producers have long used novelizations as a way to capture fans’ attention between television seasons, or installments of blockbuster film franchises. For publishers, tie-in books have become cash cows that offer instant brand recognition and access to huge fan bases for vastly larger media. One of the longest running, most successful tie-in series, the "Star Wars" novels, dates to 1976 and now has more than 125 million copies in print.

Writers and publishers of these books usually estimate that 1 or 2 percent of the total audience will buy the book, so a show that draws 2 million viewers might sell 20,000 paperback copies.

"Having that built-in audience, you don’t know that everyone’s going to show up, but you know that a certain fan will show up," said Michael Homler, an editor at St. Martin’s Press who acquired the "Sons of Anarchy" novel.

Still, in literary circles, these books have often been ignored or sneered at as mere merchandise rather than art.

"They’re treated like the lunch box or the action figure," said Max Allan Collins, who has written dozens of novelizations of shows and films, including "Saving Private Ryan," "American Gangster," and "CSI."

Lately, however, this long-maligned subgenre has taken on a patina of respectability. New writers are flocking to the form as television, in its new golden age, becomes an increasingly significant cultural medium. Rather than summarizing familiar stories, many tie-ins deliver original plot lines and subtle character development that go beyond what fans already know.

Established novelists are dabbling in the genre. Steven Charles Gould, an award-winning science fiction writer, signed on to write novels inspired by James Cameron’s blockbuster "Avatar." A few months ago, Dennis Lehane published "The Drop," a novelization based on a gangster movie he wrote, which Kirkus Reviews praised as "a sleight-of-hand novel" that’s "richer than a mere re-creation of a movie."

"With the quality of some of these shows, I don’t know if it’s fair to call them literary, but there’s a little more depth to some of them," Homler said. "The storytelling is beyond anything that’s been done before, and because of that, it lends itself well to these novelizations."

Novelizations emerged in the silent film era and grew popular in the 1930s. Before there were video rental chains or movies on demand, reverse adaptations offered a way for moviegoers to relive the experience of a film. They continued to flourish decades later and exploded in the 1970s and 1980s, when seemingly every blockbuster movie got the novel treatment. Some live on as dependable and lucrative publishing franchises. Other one-offs – based on "Howard the Duck," "Gremlins" and "Ferris Bueller’s Day Off" – were quickly forgotten.

In recent years, with the abundance of high quality television and fans’ bottomless appetite for bonus content about their favorite shows, tie-in books are evolving to keep pace.

"We’re getting more original novels based on existing franchises," said Lee Goldberg, a novelist and co-founder of the International Association of Media Tie-In Writers, a professional organization with around 250 members. "Novelizations of the films are often loved more than the films," he added.

Andrew Martin, the publisher of Minotaur Books, said he was skeptical at first when the reverse adaptation of "Broadchurch," written by Erin Kelly, was submitted.

"We just don’t do those kinds of books," he said.

But he knew Kelly’s reputation as a top-notch suspense writer and felt the book offered a different, internal perspective on the investigation of a boy’s murder.

"I wasn’t at all shy about making changes," Kelly said. "I decided that was the only way to make this work."

In his three adaptations of the moody Danish police procedural, "The Killing," the British novelist David Hewson made major changes to the show’s sometimes controversial plot twists and cliffhangers.

"I took the attitude that I was employed to write a good book. I wasn’t doing a souvenir brochure for fans of the TV show," he said.

The job still has its drawbacks. The writers often labor under impossible deadlines; the pay is modest, and writers typically have no claim to the intellectual property rights.

When Golden was approached by Sutter and FX to write the first novel based on "Sons of Anarchy," a show he loves, he couldn’t resist. He said he makes more money on his original novels than on tie-in books, which typically bring in a five-figure advance, but nevertheless finds it hard to turn them down because "the 15-year-old me would be furious if I said no."

He has published about 30 tie-ins, including novels based on "Buffy the Vampire Slayer," "X-Men" and "Alien."

Sutter shaped the novel at every stage and isn’t shy about taking credit. He helped determine when the story would take place (Golden initially proposed a prequel, but Sutter rejected that idea), approved the plot outline and adjusted some scenes. A member of Sutter’s writing team proofread the novels to make sure all the details, like the length of the protagonist Jax’s hair, matched up with the show. St. Martin’s gave the novel a big push, with an announced first printing of 100,000 copies and a social media campaign targeting the show’s 8 million-plus Facebook fans and its more than 660,000 Twitter followers.

"Sometimes I meet writers who are like, ‘Why are you doing this?’ but I would be betraying who I am if I said I’m never going to do this again because it’s beneath me as an artist," Golden said. "I combat the idea that these can’t be good novels."

Alexandra Alter, New York Times

© 2015 The New York Times Company