There are other, obvious things that unite them — such as being mother and son, no small bond — but what brought Iris and Roy Johansen together as writers was … submarines.

“We kept saying ‘We’ve got to write something together,’ ” says Iris Johansen, the prolific author of contemporary and historical romance novels as well as 17 popular works of suspense, including the bestselling Eve Duncan series.

“We have similar styles — we both write by the seat of our pants — but it was very difficult to find a vehicle that could please him and me too. … Then one day he came back from Chicago, and he said, ‘Mom, I found it!’ I said, ‘What?’ He said: ‘Submarines!’ I said, ‘Wait, Roy, I have to tell you — I’m not Tom Clancy.’ ”

But Roy Johansen’s trip to the Windy City’s Museum of Science and Industry, which has a German sub captured in World War II on display, paid off handsomely. It inspired the pair’s first novel together, Silent Thunder, about a marine architect who discovers a dangerous secret while preparing a decommissioned Soviet sub for an exhibit. A sequel, Shadow Zone, was published two years later, after the standalone Storm Cycle.

The Johansens come to Books & Books in Coral Gables Tuesday to talk about their fourth collaboration, Close Your Eyes (St. Martin’s, $27.99), a thriller about a music teacher whose sight has been restored through stem cell surgery. Being blind, though, has had one advantage; it has allowed smart, observant Kendra Michaels to perfect her other senses. She’s a problem-solver who’s an impressive weapon, and the FBI enlists her to help with an investigation into an agent’s disappearance. He just happens to be Kendra’s ex.

“She’s a unique character,” says Roy Johansen, 52, a screenwriter and Edgar Award-winning author of the novels Deadly Visions, Beyond Belief and The Answer Man. “We had a lot of fun with that, having her walk into a room and know everything about people. … but it has to mean something to the overall plot of the story. It has to have some purpose, to push the story forward constantly.”

The Johansens introduced Kendra in the short story With Open Eyes (available digitally). Now, they shake their heads ruefully over their naïveté about short-story writing.

“We had never written a short story, and we thought, ‘We’ll just toss that off,’ ” says Iris, 74, starting to laugh. “We had to introduce her and her particular powers. … I kept saying, ‘Can’t we have 50 pages? What about 60?’ ”

Roy agrees: “It was so hard! We spent weeks and weeks, a couple of months trying to get that right.”

You might think residing on opposite sides of the country — Roy lives in Los Angeles, and Iris lives outside of Atlanta — would make collaborating difficult, but the Johansens have perfected their system (with daughter and sister Tamera acting as Iris’ research assistant). One of them comes up with an idea, and they spend some time discussing it. Specifics come later. They agree on a concept, and one of them will write 70 or 80 pages, then pass the story along to the other to write the next 70 or 80 pages.