Nelson DeMille’s 21st novel is a collaboration—the first of a trilogy and the first with his son, screenwriter and film editor Alex DeMille. In The Deserter, due out from Simon & Schuster October 22, Delta Force soldier Kyle Mercer disappears from his post in Afghanistan. When he’s spotted in Caracas, Army investigators Maggie Taylor and Scott Brodie are sent on a mission to find the answers: What happened? Why? And how did he end up in this violent, chaotic city? Their assignment is to bring Mercer back alive, something complicated by Brodie’s suspicions and the partners’ inevitable mutual attraction.

We know about Nelson, a decorated Vietnam War vet who handwrites his novels on yellow legal pads with #1 pencils and has topped bestseller lists for decades. But Alex? “Seeing my dad’s creative life made me want to be a writer early on,” he tells me. “But after college, I decided that I wanted to follow in my father’s footsteps but not do the exact thing, which set me on a filmmaking course. I wanted to stay creative but different.”

After a long relationship with Grand Central and its predecessor, Warner Books, going back to the 1970s, Nelson signed a contract with Simon & Schuster in December 2014 for six books, three of them collaborations. “I wasn’t crazy about collaboration, but it was in my contract, and I started thinking about authors writing with their children, like Lisa Scottoline and Clive Cussler,” Nelson says. “And I knew Alex understood plot and structure and characters.”

S&S editor-in-chief Marysue Rucci thought the coupling was a great idea. “Alex was a successful screenwriter [he’s won several awards, including best film at San Diego Comic-Con in 2012 for The Absence], and I figured they wouldn’t stop talking to each other!”

As Jennifer Joel, Nelson’s coagent at ICM, along with Sloan Harris, puts it, “Nelson happily stumbled into realizing that the perfect partner was his son, and we knew Alex had the story chops—a win-win-win situation.”

When Alex got the call from his father (“I asked him if he wanted to make some easy money,” Nelson says, laughing), he says he was “hesitant but flattered and not sure how it would work.” Alex took on what there was at that point—the idea of a deserter, the characters, and the framework—but he changed the plot and the backstory.

“Venezuela was Alex’s idea,” Nelson says. “And he also put the spin on Brodie, making him a dangerous guy in a dangerous place.”

The move to S&S was serendipitous. Rucci had always been a DeMille fan, along with S&S publisher Jonathan Karp, and when they heard that Nelson was looking for a change, they mentioned to his agents that they were very interested. “He wanted a fresh start, and we promised him a fresh start,” Rucci says.

Nelson went to ICM in 2012. “I am a mad fan,” Harris says, while Joel calls Nelson “one of my favorite authors of all time.” Joel had met both Nelson and Alex in 2002, working at her first agency job out of college as an assistant. Years later, she saw him at BEA; he was midcontract and mentioned that he had left his agent.

Then a colleague at Curtis Brown told Harris that Nelson was indeed looking. “I mentioned it to Jenn, whose face had the same look as mine when she heard the news,” Harris says. The two of them went out to lunch with Nelson and the relationship was sealed.

“We both loved him so much that we thought it would be fun to represent him together. We wanted to understand Nelson’s aspirations; it was time for a change,” Harris says. There was a series of small meetings with different houses. “S&S was the clear victor,” she recalls. “We felt from day one that the whole building was behind him.”

The Cuban Affair, Nelson’s first standalone with S&S, debuted at #1 on several lists, including all of the New York Times bestseller lists. “Being with S&S was like a new marriage,” Nelson says. “I was a little anxious about performing, but when The Cuban Affair hit #1, it felt good. I did the best I could for me and the best I could for them.”

The Deserter feels like a Nelson book but also feels contemporary. About The Deserter, Rucci says, “I love Nelson. I love the project. I admire his work ethic; he’s a perfectionist.”

“I try to keep up with changes,” Nelson says, adding, “Alex is 35; he’s tuned into language. Kyle Mercer is his character.”

Alex gave Rucci a sketch of the book. “She didn’t ask for it, but I wanted to do that,” he says. “Marysue trusted us. She knew where to step in.”

Rucci reveals that “Nelson is not a fan of progressive editing. He likes to be finished before he gets any comments, but I got him to agree to let me see sections—by begging! It was actually grueling, because I would be left hanging waiting for the next installment.”

With The Deserter, Nelson says he hopes readers enjoy the characters and the idea of a father-son team. “I feel responsible for changing Alex’s career,” he says. “But he’s comfortable with publishing people. It’s a rare and friendly community. The movie business is very tough. Publishing is just tough.”

The pair will do a six-city book tour, early excerpts will be available through Nelson’s newsletter, and there will be giveaways and promotions on social media.

Alex is committed to two more books featuring Scott Brodie and Maggie Taylor, but he’s also working on a screenplay, and he wants to do more film editing. Nelson, however, says that he “hands the books over to Hollywood.” He tells me, “I wrote a screenplay for Word of Honor for Dino De Laurentis. I thought it was good. Dino said, ‘Nelson, it’s too much like the book!’ ”