If the summer action blockbusters are only as good as their lead stars, then the filmmakers of "XXX" are lucky that they have a man like Vin Diesel at their disposal. In a movie which asks the audience to believe that a man can swipe a senator's car and drive it off a bridge without dying, prevent a diner from being taken hostage, elude Colombian government enforcers who think he's a drug lord, and save the world from nuclear war in just under two hours (in movie time, of course), the actor has to be defined by a rather monstrous physique, otherwise the film's plausibility is overridden by unconvincing scenarios in which stunt doubles on wires pretend to look like they're pulling off dangerous tricks on a blue screen. Luckily, Diesel is a large, muscular, firm and foreboding screen presence, ideal for these kinds of physically demanding movies just as the Greeks were for the early athletics. It's nearly impossible to imagine anyone else filling the role as believably as he does.

The movie reunites Diesel with director Rob Cohen, who were both at the helm of last year's box office smash "The Fast and the Furious," about an underworld of illegal racers who modified cars to be literal speed machines. Like that film, "XXX" is glitzy and loud, full of swift adrenaline-fueled sequences that repeatedly test the eye's endurance, sometimes in mere split seconds of swiftness. The only difference, however, this time around is that both Cohen and Diesel aren't held back by a script with countless rough patches and plot holes; their material is worthy of the ambitious thrust, and once the film begins to wind down, we're engaged too much to notice that a whole 120 minutes has gone by.

Diesel stars as Xander Cage (or "X," as he is known as by his friends), a daredevil of extreme sports whose sly wit and free spirit take him into situations that no typical human being would dare to tread. As the movie opens, Xander makes a daring political statement by snatching the fancy sports vehicle of a right-wing state senator, whose hopes of banning video games and rap music don't really sit well with the thief's own ideals. With cops tailing him at every turn, camera equipment hooked onto the vehicle films him ranting on about the evils of the government system, all just shortly before he drives off a bridge and into a gorge where he parachutes to safety moments before the car implodes on impact. We instantly gather that this kind of life-threatening stuff is a popular pastime for Mr. Cage; another day, another explosion, another personal victory.

Shortly after his latest stint, Xander is apprehended by the NSA, a CIA-like U.S. intelligence firm headed by Agent Gibbons (Samuel L. Jackson). Seeking his skills as a careless stuntman, Gibbons puts him, and others like him, through a battery of difficult tests to study his endurance, speed and success rate against life-threatening situations. The reason: they need a man of this caliber to investigate Anarchy 99, a Czech-based order of rebel Russians who have top secret plans of unleashing a massive nuclear war among the world's most powerful nations. Xander's commitment to this request is nearly forced upon him, however, because of his own antigovernment ideals, but when Gibbons offers him pardons for all his capital crimes, he agrees to the task, if still somewhat reluctantly.

"XXX" (which is pronounced "Triple X") breaks no ground in terms of storytelling, plot devices or even character arcs (who else, for example, would be the object of Diesel's affection but a woman on the wrong side of the tracks?), but it pitches itself at us in a very energetic and worthwhile fashion. Not too many movies are successful at allowing their heroes to work against gravity and logic, but even fewer function without resorting to heavy special effects manipulations. As is the case with "The Fast and the Furious," what you see on screen here seems like pretty authentic stuff: the explosions, the acrobatic tricks, and even the gunplay have an anchored edge to them, as if Cohen instructed his actors to act more like war soldiers before throwing them in front of the camera. This results in quite a few rewarding action sequences throughout the two-hour experience, and there is even a sequence done on a mountain top so brilliantly that it makes typical James Bond maneuvers looks amateurish.

I won't go into any more detail about the characters or the surprises, as they're part of this endeavor's big reward. However, a couple of issues that detract from the film's performance need to be addressed, the first being the concept of Russian rebels having the sufficient resources to wage wide-scale warfare. Throughout the picture, we're told that the leader's assets have made him a powerful man in his own circuit, and yet the only real evidence we see of any of this are several underground dance clubs and a mansion with security cameras in the snowy mountains. How does this antagonist manage to keep hidden a secret lab facility for nuclear research when there are so many people working on the project? Does he just assume they'll be quiet and never slip about the detail? And doesn't anyone grasp the concept that this kind of experimenting will probably lead to their own demise? Further irritating our minds, Samuel L. Jackson appears in the movie totally scarred on one side of his face, and aside from the occasional "scar face" joke from a nearby smart alec, the script never sees the need to explain what happened to it despite it being heavily emphasized.

I am, of course, speaking about very small problems with "XXX," and that's thankful. Here is a movie in the grand tradition of the most exhilarating summer blockbusters, where action isn't exercised by artificial visuals, characters are genuinely interesting and the payoff is about more than just watching the hero blow the bad guy up into a million little pieces.