Not pretty—but it’s not trying to be. The “more than adequate” is a clue to Reacher’s psychology: he is aiming to do maximum damage. He’ s a good guy who is, with his penchant for violence, very close to being a bad guy. His code is chivalric, in the sense that he fights on behalf of the good; sometimes this means the weak and the wronged, sometimes this means the U.S. government or its proxies. His actions, though, are as unchivalric as they come. He executes opponents, kicks people when they’re down. If he gets a chance to shoot someone in the back rather than the front, he takes it. He may be a hero, but he’s a realist, too.

Any new Reacher novel fits within a grid well known to Child’s readers. There are first-person stories, narrated by Reacher himself (“Killing Floor,” “Persuader,” “Gone Tomorrow,” and three others), and third-person stories (the bulk of them). There are novels set during his Army career (“The Enemy,” “The Affair”) and novels set in the present, after Major Reacher’s honorable discharge, in 1997 (the bulk of them). There are recurring tropes and themes. The novels roam across America, with a notable affection for places in the middle, for big, blank landscapes, for small towns where no one apart from Reacher ever wants to stop. He visits rural Nebraska, rural South Dakota in winter, back-country Texas in summer. He likes communities that, to outsiders, seem nowhere in particular. Child is a poet of diners and motels, venues that capture an itinerant’s view of America. He dramatizes the lives you glimpse through a bus window, the glance into warm buildings from the cold outdoors. According to Graham Greene, Henry James once said that “a young woman with sufficient talent need only pass the mess-room windows of a Guards’ barracks and look inside in order to write a novel about the Brigade.” The Reacher novels often have that feeling, of being constructed around half-longing insights into the lives of others.

The writer whom Child most recalls, in this respect, is Georges Simenon, whose Maigret novels are the work of a man who travelled around France observing strangers and their mysterious routines. Simenon spent a lot of time in the kinds of places where travellers spend time. As a result, he set entire novels in cafés and bars, in fuggy interiors populated by secretive regulars, where the detective is an intruder. Readers find it easy to identify with this perspective: we ourselves are outsiders peeking into another world, like Reacher or Maigret.

Reacher’s character is defined by one startling device: he has no home and no belongings. He is a permanent wanderer, hopping from town to town with no aim in mind, and the novels are the story of the trouble he finds. Not only does he own nothing; he carries nothing. He doesn’t even have a bag. Clothes? He buys a new set every few days. (On the issue of Reacher’s underwear, it’s best if we just don’t go there. A 2011 survey by Clorox found that one in eight American men fails to change his underpants daily.) He is an existential hero, the apotheosis of the lone stranger, travelling the Lower Forty-eight with nothing but his folding toothbrush and his code.

Here again is the shift from implausibility to something that feels real. The alienated, possessionless freedom of Reacher has a core of emotional truth. It’s clear from the books that Reacher pays a high price for his freedom; he is lonelier and more isolated than he realizes. There is almost always a romantic interlude—“love interest” wouldn’t be the right way of putting it, but Reacher’s affairs do involve liking and lust and the not quite acknowledged appeal of a softer life. His version of freedom challenges the Superman test, but the yearning it expresses feels real. If you learn a little about the life of his creator, you’ll find a hint as to why.

When Lee Child began writing the books, he wasn’t Lee Child; he was an English television exec named Jim Grant, about to be laid off from his work at a provincial TV company in the northwest of England. Grant knew that he was going to be sacked, so on September 1, 1995, he went out and bought three notepads and a pencil, and used them to work on the book that was to become “Killing Floor”—and he has begun work on a new novel on the anniversary of that day every year since. In the course of those twenty-one years, the Midlander Jim Grant has become the U.S. thriller writer Lee Child, whose creation, Jack Reacher, has topped the New York Times best-seller list eleven times. It is an extraordinary story of reinvention, and it is, perhaps, a clue to the emotional armature of Reacher—a character who, to his creator, is very real. “When he writes,” the scholar Andy Martin has observed, “he goes into a ‘zone’ in which he really believes that the nonexistent Jack Reacher is temporarily existent.” As Child puts it, “The novels are really reportage.” If this were a proposition in logic, you would say that Lee Child is to Jim Grant as Jack Reacher is to Lee Child: the incarnated idea of freedom.

Within that freedom, the Reacher novels are variations on a set of themes: “the same but different,” as Child says. One of the books’ great pleasures is following Reacher’s turns of thought. Set-piece fight scenes are one of the fixed points of Child’s work; the other is its opposite, Reacher’s thought processes as he figures out who the bad guys are and what’s going on. That’s the usual setup: we know that something is happening, but we don’t know exactly what, and we don’t know who’s behind it.

It’s hard to convey just how seductive following Reacher’s thought can be. This is the appeal of most good detective fiction, from Sherlock Holmes on, but there aren’t many writers who have made the process seem as real, as close to actual thinking, as Child has. A hint of how he does it came last fall, in the form of “Reacher Said Nothing: Lee Child and the Making of Make Me,” by the aforementioned Andy Martin, an academic from the University of Cambridge with an unusual portfolio of interests (he has published books on surfing, existentialism, Jules Verne), which includes being a Lee Child superfan. Martin persuaded Child to let him sit in on the writing of his previous novel, “Make Me,” and the upshot was that he literally sat there, in the room, while Child was writing the book. He was there on September 1st, when Child index-finger-typed its very first lines: