In Forsyth’s The Fox (Putnam, Oct.), MI6 employs the talents of 18-year-old genius hacker Luke Jennings against Britain’s enemies.

Is there a real-life basis for Luke?

Yes, there is. In fact, over here in Britain, we’ve had two such people. The first did exactly what Luke did. He broke into the American NSA databases, one of the most secretive and impenetrable databases in the world. The Americans were seriously worried about the damage this kid had done and wanted him extradited. Prime Minister Theresa May, who at the time was home secretary, saved him. She didn’t extradite due to his fragile mental state, as she didn’t think he’d survive in a Supermax prison, which is where he was destined to go.

Do you think intelligence professionals pick up ideas from novels and use them in their work?

Apparently they do, even if they say they wouldn’t rely on fiction. Once, during the Cold War, I was interviewing a high-ranking defector from the KGB. I introduced myself, and he said he knew who I was and that I was very popular. I thought I was banned in the USSR, and he said I was to the people but not the KGB, and that every time one of my books came out they had a limousine from the embassy outside a bookshop in London to pick up 50 copies. After their shipment in a diplomatic bag to the Russian equivalent of Langley, there would be two to three days of silence, as all the generals were busy reading.

In your 2015 memoir, My Life in Intrigue, you said you wrote The Day of the Jackal in 35 days. Do you still write at that speed?

No. I was 31 then, and I’m now 80. Jackal was all prepared in my head, as I had lived through being a foreign correspondent in Paris in 1962–1963. The OAS was on the threshold of assassinating the president of France. Even at the time, I didn’t think they would succeed unless they hired a real pro with a sniper rifle. Seven years later, I went back to that thought. I didn’t do any preparation and wrote off the top of my head, producing 10 pages per day over 35 days, which became a novel. The only thing I researched was how to forge a British passport.

You once announced you were retiring, then you changed your mind. Is this the last book you’ll write?

This really is the last! I wrote this the same year I moved houses, which is traumatic enough, and the tight deadline nearly knocked me sideways. I was writing frenziedly fast from March to May. Age has certain privileges, and one is that you’re allowed to slow down.