At Risk has an impressive hook for readers who prefer their thrillers to be quick, intense and above all realistic: it was written by Stella Rimington, who joined Britain’s Secret Service (MI5) in 1969 and served as its director general from 1992 to 1996. In her MI5 career, she worked in counter-subversion, counter-espionage and counter-terrorism. It’s hard to imagine a writer better prepared to produce an MI5 thriller that rings of authenticity.

Happily, Rimington turns out to be a pretty good writer, too. She’s alert to setting and character details, her dialogue is fairly strong (if a little staged in its comic touches), her plot is compelling, and she keeps the pace up. That’s most of the battle for a thriller, isn’t it?

Perhaps more importantly, though, Rimington has created a protagonist who is engaging enough to make a strong reading companion.

Liz Carlyle is a 37-year-old intelligence officer notable both for her strong work ethic and her admirable tendency to tweak the bland and the boorish. (She gets a subtle thrill from wearing slightly risqué clothes in a workplace filled with relatively drab co-workers, for instance.) She doesn’t approach her job the way her superiors might always like, and she certainly doesn’t pursue the life her mother would wish for her, either. (She’s secretly having an affair with a married man, and there’s no prospect for a sheltered life in the suburbs anytime soon.)

She’s not happy with her situation, though, and she’s mulling some life changes when a potentially catastrophic situation begins to form. Signals from abroad suggest that an Islamic terrorist organization is about stage an attack, somewhere in England. The fact that an ‘invisible’ — “CIA-speak for the ultimate nightmare: the terrorist who, because he or she is an ethnic native if the target country, can cross its borders unchecked, move around the country unquestioned, and infiltrate its institutions with ease” — may be utilized in the attack makes the investigation especially difficult.

Slowly, clues appear. A fake British driver’s license purchased in Germany in the name of a known associate of terrorists seems connected to the tip that a person of interest may have been smuggled into the country from Germany. But is that person the invisible or merely an accomplice? And where will they strike?

It’s a jigsaw puzzle of a plot, with Rimington offering pieces one by one right up to the book’s last pages. Only rarely do we get ahead of her in the guessing game. Like many Hitchcock films, this is a thriller about ‘where’ and ‘what’ far more than it is ‘who’ (or even ‘when’), and Rimington keeps us gloriously in the dark, even though we know it must end with MI5 on top.

At Risk is a strong debut that, with its insider’s look at the office politics (and gender wars) inside MI5, offers a little more than the standard thriller typically offers. Hopefully, Rimington will produce a second thriller with Liz as its center — she is certainly interesting enough to carry a series.