What the hell was that?!

Director Christopher Nolan’s “Tenet” finally arrives in theaters Thursday, and watching it one thing is immediately clear: The months-long shroud of secrecy around the film’s plot was not for fear of spoilers, but rather because Warner Bros. couldn’t find a smart enough marketer to summarize this science blither-blather.

Even for the vaunted director of “Inception,” an epic about shared dreams, and “Memento,” in which scenes play out in reverse, “Tenet” is heady stuff. Trying to understand the story can make you feel like you’re sitting on a stool in a dunce cap.

The points I’m confident about: The main characters are trying to save the world from total annihilation; the leading man is romantically interested in Kat (Elizabeth Debicki), a British art dealer married to a weapons dealer (did they meet in dealing school?); and the film is, in the broadest possible terms, about time travel.

The rest is murky.

Nolan’s most irritating choice is to name John David Washington’s leading man The Protagonist. Are we in Physics or Lit Class, Chris? He’s a CIA agent, who after nearly dying on a mission in Ukraine, is given a new life on a secret team called Tenet.

Tenet’s scientists have discovered mysterious objects, such as bullets, that can move backward through time. These anomalies, they believe, were developed hundreds of years in the future as weapons to fight a cataclysmic war, like a Terminator without pecs or an Austrian accent. “Inverted,” they call them.

“Don’t try to understand it,” The Protagonist is told. “Feel it.” Nolan is delivering a PSA to his perplexed audience as well.

The inverted weapons have fallen into the wrong hands, which leads the Protagonist through a seedy network of arms dealers in Mumbai, London and luxe yachts on the Amalfi Coast. He teams up with Neil, played by a wisecracking Robert Pattinson. The Brit, who channels Dudley Moore, gets better with every role.

The frame is simple enough. But contained within its James Bondian plot is an endless series of unanswered questions. After the movie debuted in Europe, some commenters said it makes more sense after rewatching it. But that’s a cop-out. Just about everything in life is better the second time. We shouldn’t have to drop another $15 to appreciate the nuances.

With too many long stretches that beg the question, “What on earth is going on?” your first experience with “Tenet” won’t leave you satisfied.

Still, we’re swept up by Nolan’s incomparable cinematic vision. He is one of the few directors working today who consistently churns out visually seismic, sophisticated action films — a genre that’s become dumb as a Wahlberg.

The chases and combat of “Tenet” — featuring fighters who are in our forward-moving present, and others who are inverted, or battling backwards — are sensational. Even the basic sequences are terrific. Washington takes a cheese grater to a bad guy’s face.

A certifiable badass, Washington’s character, not by his own fault, is too unflappable. He’s calm and collected, and speaks like Spock, but could use some doubt and fear to humanize him. Spike Lee’s gutsier film, “BlackKklansman” showed him off much better. Debicki is good, if a dead ringer for Emily Blunt, and wears her peril on her sleeve. And as her scary Soviet husband, Kenneth Branagh does his most honest work in ages.

Nolan, who has become a regular in the Oscars race, is probably not going to get a nod for this one. But kudos for him, these last few months, for being a champion of the movies.