RUTHFULLY YOURS

The point is made and the scene moves on—but during a conversation over coffee at Chicago’s Four Seasons Hotel, where Mr. DeMille is staying during a nationwide book tour, the author muses on the root of the problem. His mind turns to Alexander Solzhenitsyn, the Russian author and dissident, who died in 2008. “Intellectuals said socialism is good if you do it right. Solzhenitsyn said: No, it’s coercive by its nature. There are millions of people in the world and in this country who don’t know that. They can even visit Cuba and not change their thinking one iota,” Mr. DeMille says. “They are intellectually or emotionally tied to some kind of ideal.”

They’re also easy to lampoon—and Mr. DeMille’s wit is on full display in “The Cuban Affair,” his 20th major suspense novel, following the likes of “Plum Island” (1997) and “The General’s Daughter” (1992), the latter adapted as a 1999 movie starring John Travolta. The new book came out Sept. 19 and is on the fiction best-seller lists. Mr. DeMille calls it “an old-fashioned chase-and-escape action adventure.” Its Cold War theme echoes “The Charm School” (1988), perhaps Mr. DeMille’s best-known novel.

Mr. DeMille, 74, was born in Queens and grew up on Long Island, where he still lives. In 1966 he was a student at Hofstra University: “I was kind of bored at school and didn’t sign up for the spring semester.” He received a draft notice, enlisted in the Army, and attended officer candidate school. Then he shipped off to Vietnam, where he saw combat as a platoon leader during the Tet Offensive. After three years in uniform, he returned home, finished his degree, and tried to write what he calls “the Great American war novel.”

A book editor told him nobody wanted to read about Vietnam. So Mr. DeMille switched to police procedurals, pumping out six cheap paperbacks. He didn’t make much money, but he sensed he was in the right place: “If you’re a painter and you’re living in Paris in the 1920s, you’re where you need to be. If you’re a writer, you need to be in New York. I don’t care if anybody else says, ‘Yes, you can do it from your farmhouse in Dubuque.’ Being in New York helped.” Under pen names, he wrote a biography of Barbara Walters (as Ellen Kay ) and a fictionalized book on sharks (as Brad Matthews ). “That’s when ‘Jaws’ was out,” he explains. “It was on-the-job training. I was learning my craft.”

When a talent-spotting publisher advanced him a five-figure check, he began to draft “By the Rivers of Babylon,” the 1978 novel that became his first hardcover book—and also one of the first thrillers to take on Middle Eastern terrorism. Since then, Mr. DeMille has written a novel roughly every other year, selling tens of millions of copies. He’s in talks to turn the tales of one character—a New York police detective called John Corey, the hero of seven books—into a television show.

“I’ve been offered bonuses to write faster,” says Mr. DeMille. Many big-name novelists publish annually, encouraging fans to mark release dates on their calendars as if celebrating a birthday. Not Mr. DeMille. “To do a book a year every year is just incomprehensible to me,” he says. “The quality would suffer. Stephen King can do it. He’s a brilliant storyteller. Other writers aren’t doing their best because they’re rushing it.”

Mr. DeMille likes to tell a joke—I heard it twice, during our afternoon conversation and then during an on-stage interview at an evening event in Arlington Heights, Ill. It involves James Patterson, a friend of Mr. DeMille’s who is famous for his commercial success, aided by co-authors who help him publish at a dizzying clip: “I called James the other day and his wife picked up. She said her husband couldn’t come to the phone because he was working on a book. I said, ‘That’s OK, I’ll hold.’ ”

Contributing to Mr. DeMille’s slow pace is his aversion to technology. He composes his books with a pencil in longhand; assistants decipher his handwriting and type it up for him. He makes revisions by marking on the printed pages. He owns a flip phone and says he doesn’t use the internet much.

For a man so set in his ways, “The Cuban Affair” represents quite a change. After his last book, “Radiant Angel,” came out in 2015, Mr. DeMille thought about calling it quits. “My sales had flattened at a high plateau,” he says. “That’s a reason to stay in the business—and also a reason to get out. I was vacillating.” He changed agents, left his longtime publisher, and signed a three-book deal with Simon & Schuster. “I felt a lot of the old enthusiasm again,” he says.

He also invented a new character, Daniel Graham “Mac” MacCormick, a wisecracking veteran of the war in Afghanistan who runs a charter-boat business in Key West, Fla. “A lot of characters from my past books are approaching Social Security age,” Mr. DeMille says. “The magic number in Hollywood and popular fiction seems to be about 35 years old.” For insights into the mind of a character less than half his age, Mr. DeMille consulted his son, a 37-year-old screenwriter.

Before that, however, he settled on the book’s main locale: Cuba. “It’s a Cold War time warp, an anachronism,” he says. “It’s hard to believe it’s still there, with a political system that’s not working. How do these people who have so many contacts with friends and family in South Florida and know exactly what’s going on in the states—the prosperity, comfort and political freedoms—how do they tolerate the system?”

As he discusses Cuba, Mr. DeMille mentions the Soviet Union. He traveled there in the ’80s before writing “The Charm School.” A character in that novel predicts that it would be a decade before the Soviet Union went belly up. “That was wrong,” the author now acknowledges. The Berlin Wall came down the year after the book was published. Mr. DeMille refuses to make a similar guess about Cuba’s future, even though he visited the island for research in 2015. “Cuba just kind of creeps on,” he says. “After communism collapsed around the world, this place held on. Maybe it was the charisma of Fidel Castro ? I have no idea. I have no answers.”

The Cuban people, though, impressed him. One scene in “The Cuban Affair” takes place in a chop shop, where Havana’s ingenious auto mechanics make classic cars run with old parts. On his trip, Mr. DeMille also spotted more-mundane examples of resourcefulness: “Everybody’s got a line in the water to fish. That’s where their protein comes from.” He’d like to see more of this spirit, but knows that the government won’t allow it. “Cuba’s not evolving the way Vietnam has,” he says, recounting a trip to Southeast Asia in the 1990s as he researched “Up Country,” a 2002 novel. “The Vietnamese have embraced capitalism wholeheartedly.”

Things are different in Cuba. “In case anybody is wondering, socialism just doesn’t work,” Mr. DeMille says. “This is a dictatorship. It’s an oppressive police state. They have no property rights. People stand in line to gather the necessities of life, like food and clothes, wasting millions of hours. It comes down to wasted lives.” In “The Cuban Affair,” Mac surveys the decayed grandeur of Havana and concludes: “This whole city needed Cuban American contractors from Florida.”

Will the people ever rise up against their tormentors? “Cuba is known for its revolutions,” Mr. DeMille says. “Now when they need one, they can’t seem to get it together.” At the event in Arlington Heights, holding a Cuba libre—rum and Coke with lime—he sums up his research trip: “I couldn’t wait to get to Cuba, and then I couldn’t wait to get out of there.”

Mr. DeMille calls himself “an old Rockefeller Republican” and says he voted for Donald Trump. “Americans saw a man with cojones, someone who was going to stand up for this country. I compare him to Teddy Roosevelt : He’s a brash New Yorker, a man’s man.” On Cuba, he thinks Mr. Trump has an opportunity to emerge as a statesman: “Trump could go to Cuba, like Nixon went to China. Obama going to Cuba was like carrying coals to Newcastle.”

Of all the books he has written, Mr. DeMille’s favorite is “The Gold Coast,” released in 1990. The story involves a clash between a New York aristocrat and a Mafia boss. Many readers compare it to “The Great Gatsby”—if not for its artistry, at least for its Long Island milieu. Mr. DeMille clearly enjoys when readers make this connection, though he confesses he’s no fan of F. Scott Fitzgerald : “His writing style was almost Edwardian, not that modern crisp style of Ernest Hemingway. ” Hemingway’s home near Havana makes a brief appearance in “The Cuban Affair.”

The most obvious literary link to “The Cuban Affair” is “Our Man in Havana,” the 1958 espionage novel by Graham Greene. Mr. DeMille says that as he prepared to write “The Cuban Affair,” he reread Greene’s book—but also that he avoided any mention of it in the novel because of how readers have changed over time. “I don’t want to lose an audience that might not understand literary allusions or historical references,” he says. “In the 1970s, you could make shortcuts and talk about World War II or even World War I and readers would get it. Readers today don’t have the same classical education. I refuse to dumb down my books, but I make accommodations by avoiding some issues and subjects that might not resonate.”

Mr. DeMille finds this regrettable. “I had a good liberal-arts education,” he says. “It spurred me to read more and more. Students had conversations about poetry and took some pride in that, especially the ones who were the first in their family to go to college. They wanted to be intellectual. Now it’s gender studies.”

It’s reminiscent of that joke at the expense of the Yalies in “The Cuban Affair.” Mr. DeMille says: “It’s easy to poke fun at politically correct people—so much so it’s not worth it anymore.” When I point out that he hasn’t kicked the habit, he makes a quick reply: “I could do more of it.”

Mr. Miller is director of the Dow Journalism Program at Hillsdale College and host of “The Great Books” podcast for National Review.