Tom Cruiseis nuts.

In “Mission: Impossible — Dead Reckoning Part One,” he drives a motorcycle off a cliff, straight down into a rocky canyon, then pulls the ripcord on a parachute.

No one else would do this, not even for Tom Cruise’s money, andhedoesn’t need to do it, because he alreadyhashis money. As a stunt, it’s the most remarkable thing anyone has ever done in a narrative feature and survived. We have computers these days, so he could have faked it. Why bother doing it?

The answer is obvious: He did it forme.He may have done it for you, too, but in any case, he did it so I can watch and know it’s real. A CGI stunt would have looked just as good — it might even have looked better — but it would have been fake. And it certainly could not have been the glorious thing it turned out to be, which is the largest and most bizarre act of generosity ever executed by a performer on behalf of a mass audience.

The fact that driving off a cliff is almost classically ludicrous only makes the gesture more pure. The fact that Cruise did it at 58, an age when human beings are famously more sane than brave, makes it even better.

But best of all, he did it in 2020, as the first thing shot for the movie, and we all remember what happened that year, right? At a time when the whole world was staying inside, frightened, Cruise was driving off a cliff and doing it, not just fearlessly, but cheerfully. He was expressing possibility and the joy of survival.

This is what Tom Cruise has come to represent and embody in movies.

As a film, “Dead Reckoning Part One” is a sturdy, fun, entertaining entry in the ongoing “Mission Impossible” series. It’s one of the better ones, if not quite in the exalted league of“使命:不可能的——影响” (2018). What the new movie lacks is a specific villain, though that could be interpreted as timely.

The bad guy here is an Artificial Intelligence, known as the Entity. The Entity could destroy everything. The Entity knows what Ethan Hunt (Cruise) is thinking before he thinks it. And there are some very bad people who want to control the Entity and, thus, the world.

But, as in “Indiana Jones and the Dial of Destiny” and at least three other movies in the past five years, nobody can control anything without … the key. The key is in two pieces, and so the whole movie consists of various people, good and bad, either looking for both halves of the key or trying to prevent the other from getting the key.

So, we have a vague, nebulous villain and an uninspired, unoriginal story. We also have Ethan Hunt and his team of merry geniuses (Ving Rhames, Simon Pegg) working to prevent the destruction of everything, which is too big a catastrophe for a viewer to imagine or fear.

Why, then, is this 163-minute movie worth seeing?

It’s worth seeing because每一个如果ngle sequence in it is well-made, from Ethan’s rescue of Ilsa (Rebecca Ferguson) in the desert, to the street fights in the narrow alleys of Venice, to the car chase through Rome, to the chase on foot through a busy airport. The story may be phoned in, but the planning and filmmaking are meticulous.

Incredibly, Cruise’s cliff jump isn’t the most exciting thing in the movie. Rather, it’s the extended sequence in which Ethan and Grace (Hayley Atwell) are trying to escape a train that’s in the slow process of falling into a ravine, one car at a time. It has to be counted as among the very best stunts in the entire series.

“Mission: Impossible — Dead Reckoning Part One” may not be a great movie, but it’s a special movie deserving of its own kind of event and worth appreciating. Only Tom Cruise makes movies like this, and you either understand why this is pretty wonderful or you should give yourself the chance to find out why.

Reach Mick LaSalle: mlasalle@sfchronicle.com