That’s what makes my plane rides tolerable, but it’s amazing how many books try to fulfill these criteria and fail miserably. Picking among the hundreds of tomes in the Mystery section in the Barnes & Noble is an odds-against crapshoot. Most of the brightly colored spines bind pop fiction that doesn’t pop or tired replays of what we’ve read a zillion times before. That’s why we cherish our favorites–the Stephen Hunters and Michael Connellys and John Sandfords who can dependably draw us into their worlds while our seatmates suffer with the in-flight movies. A new volume in a series with one of our beloved, tortured heroes coping with some gruesome crime is more valuable than a 100,000 frequent-flier miles. And when we discover a new author who delivers the goods (or, even better, someone who’s been churning out gems hitherto under our radar), it’s like Christmas at 35,000 feet.

That’s the way I felt when I first read Lee Child a couple of years ago. Though Child’s biography pegs him as a British former television director, he somehow has managed to create Jack Reacher: an unforgettable hero whose defining trait is his background as a West Point grad and a former Army law enforcer. Why a cop? As Reacher once said, “Because cops put things right.”

Though some of his characteristics are straight out of tough-guy central casting (you’d trust him with your toddler but he can cripple you without a second thought–check … wants to be left alone but is roused to action at injustice–check … not trolling for companionship but does more than all right with the ladies–check.), he does bring some fresh attributes to the party. Foremost is the unflinching analytical intelligence of a lifer who rose (and fell) in the ranks of the military police. Some of the best parts of any Reacher novel are smart, starkly rendered passages of ratiocination that break down a crime scene or a perp’s behavior.

Reacher’s other signature trait, though sometimes Child lays it on a bit thick, is his empty restlessness. Jobless and unattached, he drifts from place to place, learning about the country he never got a chance to experience as a military brat growing up overseas. Cut loose by force reduction, he’s homeless, but stubbornly rooted in the moral code of an institution that had no more use for him.

Child isn’t without his flaws. All too often we are expected to ignore a hole in the plot so large you can drive a Humvee through it. (Typical example: when Reacher’s brother Joe, a top Treasury operative, is murdered in the series opener, the response from the agency is so tepid it beggars credulity.) Sometimes the violence is sadistically gratuitous. But each time out, the Reacher novels are distinguished by pithy concise prose and a gripping, methodical unraveling of some grand evil scheme, with lots of fireworks along the way.

Still, as Child methodically churned out his annual installments I began to worry about the Reacher series. Last year was supposed to be a watershed, as Child had signed a fat contract with a new publisher and received heavy promotion. But “Persuader,” though as easy a read as any of its predecessors, showed signs of, well, reaching. At the center of its plot was the hero’s attempt to rescue a woman held as a prisoner by her family–the same type of mission that he’d had taken on only a couple of books previous. As is usually the case with Reacher, it was a case of trouble finding him. The formula still worked, but it was getting a trifle stale.

Now comes “The Enemy” (400 pages. Delacorte. $25.), and all is forgiven. It may be the best Reacher book yet. The big surprise is that with the eighth book in the series, we’re zipped back chronologically to New Year’s Eve 1990, when Reacher was still a military cop. I don’t know whether this was part of Child’s master plan all along, but the idea of a prequel breathes fresh air into the saga. The pace is brisk from the get-go, when Reacher, who has mysteriously been transferred from the search for Noriega in Panama to a base in North Carolina, tries to unravel the circumstances of a general’s death from a heart attack in a seedy motel.

While the coronary is genuine, the general, who was on his way to a secret meeting is no longer accompanied by his briefcase. When Reacher asks whether it contained the conference agenda, he is told that there was none. This was an answer he could not accept. In the Army, he notes, for the slightest meeting, “there’s always an agenda.” We readers, of course, just know we’re going to find out what it is, but not after a whole lot of complications. Sure enough, in his quest–which, in another thriller convention, is conducted against the orders of his weaselly new commanding officer–he tangles with civilians, the Delta Force and the aforementioned CO as he investigates a case that quickly includes the murders of folks in and out of the military. He bonds with his ambitious female lieutenant, who joins him in the search and the sack. He gets arrested, twice, for going AWOL. He visits his dying mother in Paris and learns a secret about himself. All good stuff.

For a British TV guy, Child knows a lot about the American military. Reacher, speaking in the first person, tells us how to read the story behind the “fruit salad” of medals worn on the chest, how to use military status to get an airline upgrade and why sergeants are the best thing in the Army. Every detail rings with authority. And though the book was written well before this year’s events in Iraq, there are some insights into what happened at Abu Ghraib prison. At one point, explaining a murder with sexual overtones, a Psy-Ops officer explains to Reacher what we teach our soldiers, “Impugning an enemy’s sexuality is the whole point of our course. His sexual orientation, his virility, his capability, his capacity. It’s a core tactic. It always has been, everywhere, throughout history.” Hmm.

Reacher’s investigation ends in a jarring, unexpected confrontation that exposes his own brutality, and which is totally satisfying. The bad guys get their due, but the baddest guys–the brutes who really run things–are still in charge, and grunts like Reacher have to make the best of things.

I don’t know where Child takes Reacher from here. Since the timeline of the novels has Reacher still in the Army for a few years before he takes to the road in the early 1990s, we may see another prequel, perhaps set in Desert Storm. Or we may rejoin him as he was at the end of “Persuader,” crusing down I-95 in someone else’s Cadillac. Maybe now that the Army is once again strapped for soldiers, he’ll re-enlist. Our forces in Iraq–as well as a growing legion of readers–could do a lot worse than being reinforced by Jack Reacher.

This is the first in my own series, a string of columns devoted to quality airplane reading. If you’ve got suggestions for terrific authors I might have missed, or just want to comment on your own experiences with the gumshoes and spooks you’ve encountered while squeezed into the middle seat, I welcome your e-mails.