When did you discover the activity that makes you feel most alive? When did you stop doing it?

As I read books by great story tellers about exciting, fictional heroes, I’m struck that the characters we enjoy most are often the people we set out to be but stopped being.

Some of us were deterred by well meant advice, “You’ll never make a living as a cowboy, fireman, writer … You need to have a real plan for a real job.” Or the always helpful, “There isn’t anyone who’s life is really like James Bond’s or Spenser’s or Jack Reacher’s.”

But real people do become successful, happy cowboys, fireman and writers. And at least one person, Matthew Dunn has lived James Bond’s life.

“Spycatcher” by Matthew Dunn (William Morrow, $25.99, 432 pages, hard cover). www.harpercollins.com.

A British MI6 field operative (bureaucratic speak for “spy”) Dunn recruited and ran agents. Worked deep undercover, all over the world, in hostile environments, risking execution … or worse. During his career he successfully completed about 70 missions.

British government policy precludes awarding medals to men like Dunn, but he did get a rare personal commendation for an “operation deemed to have directly influenced the successful conclusion of a major international incident.” (Bureaucraticeze for “he saved the flippin’ world.”)

Dunn’s years of toil give him unique professional knowledge that is sure to make “Spycatcher” an international best seller.

Dunn’s hero, Will Cochrane is an experienced, scarred spy who doesn’t enjoy playing by the rules. He gets jobs that must be done, done. A known wild card, his bosses believe he’s the perfect weapon to bring down an international terrorist mastermind.

The action races across Europe and the USA with Will working to prevent an attack the likes of which the world has never seen.

“The Lion” by Nelson DeMille (Grand Central, $14.99, 436 pages, soft cover). www.nelsondemille.net

Before “The Lion” way back in 2000, there was, “The Lion’s Game” an instant international bestseller. In “Lion” FBI Special Agent John Corey returns as part of our governments Anti-Terrorist Task Force.

The book grabs you from page one.

“So I’m sitting in a Chevy SUV on Third Avenue, waiting for my target, a guy named Komeni Weenie or something, An Iranian gent who is Third Deputy something or other with the Iranian Mission to the United States. Actually, I have all this written down for my report, but this is off the top of my head.”

“Also off the top of my head, I’m John Corey and I’m an agent with the Federal Anti-Terrorist Task Force. I used to be a homicide detective with the NYPD, but I’m retired on disability—gunshot wounds, though my wife say I’m morally disabled—and I’ve taken this job as a contract agent with the Feds, who have more anti-terrorist money than they know how to spend intelligently.”

“The ATTF is mostly an FBI outfit, and I work out of 26 Federal Plaza, downtown, with my FBI colleagues, which includes my wife. It’s not a bad gig, and the work can be interesting, though working for the Federal government—the FBI in particular—is a challenge.”

“Speaking of FBI and challenges, my driver today is FBI Special Agent Lisa Sims, right out of Quantico by the way of East Wheatfield, Iowa, or someplace, and the tallest building she’s previously seen is a grain silo. Also she does not drive well in Manhattan, but she wants to learn. Which is why she’s sitting where I should be sitting.”

The characters, both hero and villain, plot and writing create that rare zone where your mind says, “Read, read, read!” And you keep turning pages ignoring, sleep, food, critical bodily functions and even basic requirements like brushing your teeth and bathing.

Books as brilliant as “Lion” don’t come along very often.

Given their effect on personal hygiene, that’s probably a good thing.