Warning: Major spoilers ahead for Tenet.
All I have for you is a word. Well, actually, three words: Tenet ending explained. By now you've watched Christopher Nolan's complicated spy thriller and you're left with some very big questions. Possibly because you couldn't hear important dialogue, which is why we, like others, would suggest rewatching Tenet with subtitles. To be fair, even after doing so we still aren't quite sure we understand all the details surrounding that painting. And don't even get us started on why that secret hand gesture is introduced in the beginning of the film to never be used again. However, we can hopefully help make the final moments of Tenet easier to understand.
The plot of the film is actually quite simple. It's classic Bond, James Bond fare: the Protagonist — and yes, that is his Nolan-given name — played by John David Washington, must stop the evil Russian arms dealer Andre Sator (Kenneth Branagh) from starting World War III. However, since this is from the guy who made Inception, there is also a high-falutin gimmick to makes things more interesting and let's be honest, unnecessarily confusing. In Tenet, it's time inversion, which is not the same thing as time travel. Sorry Back To The Future fans.
Time inversion allows the characters to move backwards and forwards on multiple timelines using turnstiles with clear entrances and exits so they can make sure no one ends up coming into contact with their inverted or un-inverted selves who are moving parallel with time. If they do, the world will implode. So how do you explain those backwards flying bullets? Their entropy runs backward, which to the human eye makes it look as if they're moving backwards. Tenet's resident scientist Barbara (Clémence Poésy) explains that they think it's "inverse radiation triggered by nuclear fission" that's causing this phenomenon. It was made in the future, that they know.
We later learn the mysterious formula was created by a scientist who saw how easily it could be used for evil. It's why she divided the algorithm, the physical manifestation of her formula, into nine pieces. She sent all of them back in time so that they could be hidden in different places, making it hard for anyone to reassemble the algorithm. It was her way of saving humanity from itself.
Unfortunately, Sator, with help from the future, is one piece away from destroying the world. He is what the movie calls a broker, someone who can communicate with the future. The future apparently thinks we screwed things up so a bad that it's better to just get rid of Earth all together. The mysterious organization Tenet is now working to stop him from reversing the flow of time and destroying reality. If you don't quite get it, don't worry, neither does Robert Pattinson. Besides, at the 15 minute mark, Barbara gives us permission to stop caring about all the reversing time mumbo jumbo. "Don't try to understand it, feel it," she says. For those who choose not to heed this doctor's orders, keep reading.
After crashing airplanes into secret art hangers, joy riding on numerous boats, and driving backwards on the freeway, the Protagonist learns Sator's motive for wanting to end the world. He's dying of pancreatic cancer and wants to take the world down with him. "If he can't have it, no one can," his estranged wife Kat (Elizabeth Debicki) explains. His motive echoes what he told Kat earlier in the film when she asked why he won't just let her go. "If I can't have you, no one can," he says. The big bad Sator is consistent, we'll give him that.
He's also big into fitness or at least so we thought. Sator's plan is actually tied to the FitBit-like health tracker we see him checking throughout the movie. When his heart stops, the algorithm will do its things. He's now one piece away and plans to dead drop the final piece into the Russian city where he was born. It's there he is keeping the other eight pieces.
Tenet plans a temporal pincer movement, a "time-bending tactical technique" that allows one team to move forward in time while another moves backward. No surprise, the organization is able to stop the world from ending with help from inverted Neil who takes down Sator's henchman while also getting himself shot so that un-inverted Neil can pull the Protagonist and the algorithm up before it ends the world. Kat is also able to get vengeance on her evil husband without killing all of humanity, so bonus.
In the end, Neil reveals that it's the Protagonist who, in the future, recruited him into Tenet. They've known each other for years before this mission, despite the Protagonist never having met Neil before a few days before. But, as Neil says, “You have a future in the past." When Neil walks away, revealing the medallion on his backpack, the Protagonist realizes he's the person who helped him in the opening opera house scene. He's also the guy who took a bullet for him in the final fight. Many fans wonder if this means Neil is actually dead, but others point out that the inverted and un-inverted timelines meet in the middle so he's not technically dead dead. So yeah, your guess is as good as ours.
What the ending does seem to make clear is that the Protagonist is the leader of Tenet. When he goes to take out arms dealer Priya (Dimple Kapadia), who is looking to kill Kat for knowing too much, he seemingly reveals that he set up the entire plot of the movie, controlling this past from the future. If you have a headache after all of that, we don't blame you, but if you made it this far, give yourself a pat on the back.
Of course, with any Nolan movie, the film lives on in Reddit threads that try and piece together the Tenet character timeline and theorize whether Neil is actually Kat's son. While we don't think there's enough evidence to prove that, we are willing to entertain the fan theory that Barbara is the scientist who created time inversion, but doesn't realize it yet. Maybe that will be explained in Tenet 2, which apparently could be a thing. The Protagonist is already in.