“The Equalizer: A Novel” by Michael Sloan (Thomas Dunne Books, St. Martin’s Press, 496 pgs., $26.99)

It’s been almost 30 years since Michael Sloan co-created the TV series “The Equalizer.”

Despite the passing decades, the longtime TV writer and producer had no trouble writing the first novel based on the exploits of Robert McCall, “The Equalizer.” The book, available at retail stores and online Tuesday, hits shelves a little more than a month before the release of a feature film version of the ’80s TV series starring Denzel Washington.

Sloan toyed with the idea of writing a book for several years. He owns the film and book rights to the character. When he co-created the original TV series, based on a story idea from Richard Lindheim, the studios didn’t believe anyone would ever want to see a big-screen version of a story they had watched on TV for free.

Along with writing the book, Sloan is a producer on the new feature film.

“It took about seven months to write and rewrite the book,” Sloan says. “From the time I started the first chapter to now was about a year. Once I got started, it was not hard to write on any level. I already had his voice in my head. He was the same loner kind of guy.”

In the book, McCall has retired from his role as a guardian to strangers. His quiet life as a bartender gets disrupted when he can’t stop himself from helping a hooker being unmercifully beaten.

Just like a screenplay, the book started out as an outline. By the time Sloan had done the final edit, the story changed dramatically. Sloan wants readers to get so caught up in the story they can’t stop turning pages. If a reader has to go back chapters to remember a character, he doesn’t feel as if he’s done his job.

Writing the book was a big change for Sloan. Its 200,000 words was quite a huge leap from all of the TV programs and TV movies he’s written during a career that dates to the mid-1970s.

Sloan is known for writing and producing TV projects, including, “Bionic Showdown: The Six Million Dollar Man and the Bionic Woman,” “The Return of the Six-Million-Dollar Man and the Bionic Woman,” “Kung Fu: The Legend Continues,” “Alfred Hitchcock Presents,” “The Hardy Boys/Nancy Drew Mysteries” and “Harry O.” Most recently, he’s been writing the “Mystery Woman” cable movies.

The new feature film and book happened only because of “The Equalizer” TV series. Sloan got the idea while working as a writer and producer at Universal Studios in the ’80s. During a lunch break while working on the series “B.J. and the Bear,” Lindheim suggested he should write an updated version of the TV series “Have Gun Will Travel.”

The idea of a middle-aged retired intelligence officer as a modern-day protector of the good became “The Equalizer.”