In the course of its 2 hour, 49 minute running time, Mission: Impossible — The Final Reckoning gives you two fleeting moments that suggest that, yes, even Tom Cruise is required to respect and obey the laws of physics. In the first, he’s resurfacing from the depths of an arctic sea when, cramping with the bends, he curls into a fetal position, then drifts helplessly through the icy water. Much later in the film, gravity is hurling him in the opposite direction: He plummets down through the sky and vanishes into a veil of cloud. Whoosh.

In these few seconds, you get a sense of Cruise as just another isolated, solitary human being, one more speck lost to the obscure mysteries of time and existence.

In Reckoning, the surprisingly dour second half of 2023's Dead Reckoning, Cruise — as Ethan Hunt, the super spy he’s played for nearly 30 years — has become nothing less than Atlas, eternally braced to prevent the world from sliding down and off his back. (Judging from a few brief, shirtless scenes, the 62-year-old star has done plenty of shoulder shrugs to bear up under all that weight.) Who else (the film’s characters repeatedly ask) can possibly stop the terrifying AI engine, the Entity, from gaining control of every nuclear warhead on the planet? Who else can possibly prevent Ethan’s nemesis, Gabriel (Esai Morales), in his deluded attempts to master that diabolical gizmo?

Only Ethan. Ethan, Ethan, Ethan! 

Angela Bassett’s President Sloane is so anxious for his assistance you wouldn’t be surprised if she showed up on his doorstep with a meatloaf.

If everyone needs Ethan, however, he doesn’t especially need them.  In a vigorously bruising fight scene — it involves a treadmill and a knife — he alternately gains and loses the upper hand as he fights off an assailant. But this is on a submarine — how far off can assistance be? All he has to do is shout, “Help! I’m being attacked in the fitness center! Come quick!”

It's not that Ethan is proud. He accepts his (likely final) globe-saving assignment with what appears to be a nagging, troubled humility. Cruise, strikingly, has all but abandoned the confident star power, the gleaming look in the eye that comes close to a wink, that defined his performance in seven previous outings. He still runs with blinding speed, whether crossing a bridge or exiting an airborne vehicle, but just as often he seems to be brooding in shadow, like Marlon Brando in Apocalypse Now. And his hair has grown thatchy.

Uncharacteristically, Ethan even comes close to butchering one of his many opponents: The camera spares you the details, but you hear a prolonged pummeling and watch the horrified reaction of Hayley Atwell's Grace before you glimpse a meat cleaver buried in a corpse’s chest. (It may remind you of 2005's War of the Worlds, where Cruise, required to put on a show of cold-blooded savagery, moved off camera when it came time to murder Tim Robbins.) As Ethan tries to assure Grace that he had no choice, Cruise hits a strange, ambivalent note that wobbles between desperation and comedy.

There’s nothing wrong with a performer of Cruise's stature and charisma grappling with darkness and ambiguity in this way — in the past that resulted in one of his best, most misunderstood performances, as a doctor slipping down into a moral underworld in Eyes Wide Shut. But that was a Stanley Kubrick movie. This is a Tom Cruise mega-production with a reported price tag of about $400 million. Imagine if pilot Pete "Maverick" Mitchell had just stared at oil patches on the hangar floor, searching for meaningful patterns.

Of course, you don't have to worry that Ethan won’t do whatever’s necessary, however death-defying, to destroy the Entity. That includes dangling from a plane as it takes off, making his way across the wings with breathtaking agility (and, even more important, grim determination), then fighting the pilot mano a mano.

In other words, the big action scenes, when they finally arrive, really deliver, and then some. The movie’s centerpiece — a long, silent sequence with Ethan gingerly making his through a submerged submarine — is gruelingly suspenseful, like Sandra Bullock's Gravity but with H20. It’s one of the best action scenes in the entire franchise. It's a classic unto itself.

The terrifying Entity, on the other hand, remains a dramatic abstraction, whirling around in the digital ether like a pinwheel of doom.

Bassett is quite good as the president — her performance at least seems to reflect, seriously, the stakes of mutually assured nuclear destruction. Ted Lasso's Hannah Waddingham turns up as a stern admiral with bitter memories of combat — you can understand why Waddingham wouldn't always want to rely on her comic deliciousness, but this is a thankless little role. And, once again, the superb Hayley Atwell, as Grace, doesn't get to do enough. Apart from that prolonged display of horror, she's usually seen approaching Ethan with a warm, hungry-eyed allure, like a jewelry model being introduced to a tray of diamonds.

The movie is very nearly stolen by Severance star Tramell Tillman as an American submarine captain who keeps addressing Ethan as “mister” with a clipped, subtle note of hostility. It's as if he were thinking, "M:I, my eye!"

Mission: Impossible — The Final Reckoning (PG-13) is in theaters May 23.