PW: For the American reader, would you clarify the difference between MI5 and MI6? Is it like the FBI and CIA?

Dame Stella Rimington: MI5 is our domestic security service, charged with protecting the country, while MI6 gathers foreign intelligence. So they're broadly parallel to the FBI and CIA, except that MI5 is strictly civilian—it has no police powers. It's up to the police to take action.

And that figures in your plot.

Yes. The inter-service and interpersonal relations are never simple, but they're very important. A lot of people like to pretend that everyone's always at each other's throats, and, really, it's not like that. Of course you get individuals who rub each other the wrong way, as happens with some of my characters.

How did you make the transition from Director General of MI5 to author of a thriller?

I'd always wanted to write a novel, I had lots of plots of my head, and whenever I went on holiday, I said "This time I'll do it." But there was never time. Then I wrote my autobiography [Open Secret, published in Britain in 2001], and that was the first step.

At the end of At Risk, you acknowledge that you had help with the writing—how so?

When I started the novel, I realized it was a separate skill I hadn't immediately got at my fingertips. It was easy to contrive the characters and work out what I wanted to have happen; the difficulty lay in keeping the threads together. I needed help in pulling the subplots along a consistent route through to a conclusion.

What authors have inspired you?

I'm a chronic reader of thrillers. When I was in India in the '60s, I read Kipling's Kim, about the Great Game of espionage, and that got me started. John Buchan created brilliant chases: someone's being pursued, something has to be prevented from happening, who's going to get there first? Then Dorothy Sayers, Margery Allingham, and of course John Le Carré, who I think is absolutely brilliant.

What's next for you—another Liz Carlyle thriller?

Yes, I've become very attached to her. In the new one she's still in MI5 but has moved to a different area with a different target. Some of the same characters are in it. Wetherby, her boss, and maybe more than her boss.

Any hints about the plot?

This time instead of working against terrorism she's working against nuclear proliferation. That's all I'm telling you.

You seem to like keeping secrets.

Well, I should be quite good at determining what ought to be kept secret!

You think about such scary things. How do you sleep at night?

It's different in Britain. We've been living with terrorism for many years. We had the IRA setting off bombs in the streets of London. You didn't have the experience of it until the hideous events of 9/11. So we're more able to absorb these experiences and get on with it. Of course one of the more alarming aspects is that nowadays any kind of attack is possible because we're dealing with people who are willing to commit suicide. In the old days, they wanted to escape, so there were some things they wouldn't do. That does introduce a great degree of stress and anxiety. Nonetheless, one is far more likely to get killed in a road accident than by terrorism. Besides, I know my former colleagues are very good at their jobs, so I probably sleep better in my bed than most people.