Jack Reacher is back on the screen and aficionados of the hugely successful Lee Child airport thrillers in which he appears must be hugely relieved. This time he is played not by pint-sized Tom Cruise but by someone much closer to his 6ft 5ins height: a musclebound giant called Alan Ritchson.

Not having read any of Child’s 100 million-selling oeuvre (probably because I’m bitterly envious: he’s a Midlands-born ex-media type, like me, but has a slightly larger bank balance), I can’t tell you how true to the original Ritchson is. But he plays him as if he’s on the autistic spectrum — a loner uncomfortable with too much dialogue or human emotion of any kind, who just wants to get the job done. That job is killing all the baddies.

In the first of what will presumably be many Amazon Reacher seasons he finds himself in small town Georgia, almost instantly being hauled up by the corrupt local police (Southern cops don’t seem to have evolved much since Live and Let Die) as the suspected murderer of the unidentified man found dead by the roadside.

The corpse — spoiler alert but not really: you find this out in the first episode — turns out to be Reacher’s beloved long-lost brother. Naturally enough, Reacher’s thoughts turn to dire vengeance. But meanwhile — a monosyllabic giant would be a bit boring on his own — he needs to gather a team of contrasting sidekicks, including Oscar Finlay (Malcolm Goodwin), a black, Harvard-educated detective in a tweed suit, and Roscoe Conklin (Willa Fitzgerald), a hot blonde policewoman with a delicious Southern accent who is not afraid to use her gun.

It sounds contrived, cartoonish and formulaic, which indeed it is a bit, but it’s done in so delightful a way that you really don’t mind. For example, Reacher is a white man obsessed with the blues. Black Bostonian Finlay, by amusing contrast, is passionately into epic 1970s white-boy rock: the way he bites his lip and plays air guitar to the intro to Kansas’s ‘Carry On Wayward Son’ is a joy to behold, as is Reacher’s appalled expression.

Unlike with a dark, brooding series such as Gomorrah, these notes of comedy mean you finish each episode amused and entertained rather than in the depths of depression. The violence is brutal but somehow, as when Reacher breaks the limbs of two men he has just shot in the back the better to fit their bodies into the trunk of a car, it’s charming, fun violence because Reacher enacts it with such matter-of-fact casualness. Killing baddies is just what he does.

What has been bothering me greatly about the series so far, though, is Reacher’s rippling triangular torso. He’s forever ripping off his T-shirt to expose his pecs and six pack, presumably as a sop to all the female viewers who won’t much like the violence but do enjoy the quiet bits in between. But this only exposes a gaping plot/character inconsistency: how on earth does Reacher get a body like that with no obvious effort or exercise regimen?

Ritchson has admitted in interview that it took him ages to build up the physique needed for the role (and he later got quite badly injured, requiring surgery, in the endless fight scenes). So how does Reacher do it: this square with a character who spends his life on the road, travelling by bus, staying in cheap motels, eating on the move? Not possible. To look like that you’re on endless protein shakes and raw meat and eggs and hours each day doing weights. I can buy the enormous body count and the ludicrous storylines. But the junk-food diet and the lack of an exercise routine are just ridiculously implausible, as too is the notion that Reacher is so unvain he gets his clothes out of those dumpster bins used for the homeless. No one who is not ultra-vain ends up with a body like his.

But I’m being picky here. Reacher is great fun, one of those series you look forward to and could happily binge-watch, even though you know it’s not going to add much to your quotient of brain cells. I’m certainly enjoying it a lot more at the moment than the rather grim and earnest Robert Harris adaptation over on Sky — The Fear Index — about a charmless billionaire who trades the Vix in his €40 million Geneva lakeside home but is assaulted by enemies who may exist only in his terror-warped imagination. Maybe it gets better. I’ll let you know.