Christopher Nolan’s new film, Tenet, is my favorite film of the last decade. I don’t think it’s Nolan’s best film. But it’s hard to beat Tenet in terms of sheer fun and rewatchability. More than any movie I can think of, Tenet rewards multiple viewings. I’ve lost track of how many times I’ve seen it, and I’m still noticing new things.
What follows is my exposition of the Tenet storyline, what happened and why, and what I think it means. This is directed toward people who found the movie confusing, want an explanation, and (for whatever reason) aren’t inclined to work it out themselves. It’s also directed toward other Tenet fanboys, to compare notes. But mainly it’s because I enjoyed working all this out and I wanted to share what I learned.
Obviously, here there be spoilers. I assume you’ve seen the movie at least once, so I won’t bother explaining who the characters are.
The movie begins at the Kiev opera house (actually filmed in Tallinn), where terrorists attack a concert. (Actually, as we’ll see, it’s important that we call it an opera, not a concert.) The Protagonist is waiting outside in a van with his CIA team. One of the things we eventually notice is that we never learn his name. (If there’s a deeper significance to this, I have not figured it out.) But “the Protagonist” is a bit of a mouthful, so I’m going to say that Protagonist is his name.
A bunch of fake cops (or possibly real, corrupt cops) arrive shortly. The cops are working for Sator, and probably the terrorists too. His plan is to stage a massacre and use it as a smokescreen to steal the Plutonium-241. Protagonist is wise to at least part of the scheme; his plan is for his team to pretend to be cops and to secure his contact and the 241 right under their noses. He can’t didn’t know what agency the fake cops would pretend to be with, so he’s prepared with a lot of different patches.
All the cops, and Protagonist’s team, are wearing masks. This is because of the sleeping gas they are planning to pump into the theater, but it means that Nolan can put an inverted person into the scene, and the masks he’s wearing won’t stand out to the viewer. At the end of the scene, Neil saves Protagonist by shooting his antagonist with an inverted bullet. We know that it’s Neil because of a distinctive trinket on the zipper of his rucksack. (We don’t get a close view of the trinket in the film, but in the Making-Of documentary you see that it’s a 1943 Indian coin.)
Neil must be inverted. It wouldn’t make any sense for him to be running around with an empty gun on the off chance that he might encounter an inverted bullet stuck in the wall in just the right place to shoot an enemy, when he could just as easily carry a useful loaded gun. (Also, from a narrative perspective, if he’s not inverted there’s no need for everyone to be wearing masks.) He does seem to be walking forward, but he must actually be pretending, walking backward. One thing you learn from the Making-Of documentary is that it is surprisingly easy to simulate inversion convincingly by walking backward, and a man like Neil who lives most of his life inverted would get plenty of practice.
Exactly when the opera siege takes place in Neil’s timeline is never made explicit, but it’s probably just before he meets Protagonist at the Bombay Yacht Club. (Since it takes a full day to go back a day, any other occasion would mean sacrificing a lot of Neil’s time.) Neil must have been there because earlier in his life (but later in Protagonist’s) Protagonist told him about the incident. We don’t know exactly when, but on the Magne Viking near the end Protagonist had not told him yet. Probably it’s later, after the movie ends.
Protagonist sends his team and the contact to an unfortunate end, and he gets captured, apparently by Tenet. They torture him to determine his reliability, then recruit him. Fay teaches him the secret name and gesture. After Protagonist cools his heels in a wind turbine for a few days, he gets sent to Dr. Barbara for a very cool briefing.
There are three things in this movie that I haven’t been able to make sense of yet, and two of them are in this scene. One is the notion that the detritus of a coming war might be streaming back at us, and the other is the peculiar behavior of inverted bullets. I’ll come back to both of those later. A minor point is that the inverted bullet he pulls out of the wall should be in the chamber, not the magazine.
Protagonist learns that the bullets’ material is unique to India, so he heads off to Mumbai to interrogate Sanjay Singh, a preeminent Indian arms dealer. At the Bombay Yacht Club he meets Neil for the first time. Neil knows Protagonist well, since, from his perspective, he has known Protagonist for years. Neil suggests gaining entry to Singh’s home by bungee jumping.
The bungee-jumping scene is a cool action sequence, but it’s also cool because it fits Tenet thematically. Protagonist and Neil gain entry by doing something (bungee jumping) in the reverse of how it’s usually done. Then, just to drive the point home, they exit by reversing the way they got in.
Protagonist meets Priya, who sends him on to Sir Michael Crosby, who sends him on to meet Kat. Protagonist fights some of Sator’s goons (I cringe every time he hits the goon with the cheese grater), then he meets Kat again. Kat tells him about Sator’s preoccupation with the Oslo Freeport.
This is a good occasion to note a little easter egg that Nolan dropped into the movie. The Freeports were built by Sator’s construction company Rotas. Now Rotas is Sator in reverse, but there’s more than that. The two names are the first and last rows (or columns) of the Sator square, an ancient piece of word play that was attributed mystical significance. The other rows are Arepo (the Goya forger), Tenet, and Opera (the site of the opening scene, and the word that gets Sator to pay attention to Protagonist), all key elements in the story. What’s cool about the Sator square is that it not only reads the same horizontally and vertically, but it also reads the same when rotated 180 degrees. Again, thematically very appropriate to Tenet.
(Photo by M Disdero. Creative Commons license.)
Protagonist, Neil, and Mahir stage the plane crash to get access to the central Freeport vault where they believe Sator has stored his fake Goya. (Sator, of course, is not so easily surprised, and has removed the drawing from the vault.) A broken lockpick causes trouble and they stumble into the innermost hallway gasping.
After a moment, Neil says “there’s someone in here with us.” He is correct. Inverted Neil and Kat are there, making their way to the turnstile. They just miss encountering each other.
Arriving at the turnstile, Protagonist and Neil find bullet holes in the glass from the Protagonist-on-Protagonist fight that is about to happen. If you look at the holes, you see that the cracks are growing. This tells us something important about the physics of inversion.
When an inverted person does an action to a forward object, the effect goes in the direction the actor is going, which is backward. Thus, the bullet holes propagate backward, so they are already in the glass, even though the fight hasn’t happened yet. But why are the cracks growing? The reason is this: The wall was not built with bullet holes. Even as the bullet holes are pushing backward, the undamaged wall is pushing forward. (Later, in the shipping-container exposition, Neil explains that when an inverted action is pushing against the environment, the environment dominates.) So as the bullet holes move backward, they are gradually losing out to the unbroken wall, and thereby heal. When the phenomenon is viewed forward, the cracks grow — until the inverted gunshot takes place and they disappear.
The same thing happens (in the reverse direction) when Protagonist stabs inverted-Protagonist in the arm during the fight. The stab wound propagates in Protagonist’s direction, which is forward. But, over time, the stab wound pushes against the inverted environment and heals. When viewed from inverted-Protagonist’s perspective, the stab wound appears out of nowhere, steadily worsens, and then disappears when it is inflicted.
When Protagonist and Neil are talking after the raid, Neil mentions “Feynman and Wheeler’s notion that a positron is an electron moving backwards in time.” That’s a real thing, although it really should be called Wheeler and Feynman’s notion. (I wonder if the Wheeler character is named as an homage to him.)
Protagonist goes back to India to meet Priya again. Priya wants Protagonist to use the promise of 241 to get close to Sator. We later learn that she intends for him to lose the 241, because only if Sator obtains all nine sections of the algorithm will he bring them together, so Tenet can take them. This seems staggeringly dangerous. Why not just obtain one section, such as the 241, and destroy it? Why do they need to get all nine? Whatever the reason might be, we’re not told in this movie.
Protagonist heads to Italy, meets Kat again, eventually arranges a meeting with Sator (by mentioning opera), we get a glimpse of the Sators’ terrible home life, and Kat tries to kill Sator. After Protagonist saves Sator, Kat and Protagonist have a covert conversation on the yacht. Finally, Protagonist meets with Sator in Sator’s office.
Sator tells Protagonist about his first contract, cleaning up plutonium in Stalsk-12, but we see in flashback much more than he tells. We see Sator as a young man uncovering a capsule buried in Stalsk-12. Opening it, he finds some papers and a lot of gold. Young Sator kills his friend, establishing that he has been a monster from the beginning.
After an uncomfortable scene between Kat and Sator, a helicopter arrives delivering a capsule similar to the one from the flashback. Protagonist spies on the delivery. The capsule contains inverted gold, and Protagonist watches Sator beat a man senseless for trying to steal one bar. Protagonist is caught and dragged to Sator.
Sator gives Protagonist the bloody gold bar as funding for the Tallinn heist. This is interesting for two reasons: From a plot perspective, Protagonist deliberately fumbles the bloody gold, which gives him an excuse to scrape it over the dirt from the capsule and thereby get a sample of the dirt. From a physics perspective, when Sator tosses Protagonist the gold, we see that inverted objects can be thrown and they behave like normal objects. The gold arcing through the air is reversible (meaning that entropy is neither increased nor decreased), but when the gold comes to a stop upon hitting the ground, it does increase entropy. The inverted gold doesn’t want to increase entropy, but the yacht it is colliding with is much larger, so the yacht’s direction predominates.
In the next scene, Protagonist asks Neil about the soil samples, but it seems they did not learn anything useful. The two also discuss how Sator is receiving the gold via dead drops. The idea is that Sator buries a capsule and notifies the future where it is buried. The future then fills it with inverted gold, which goes backward to Sator’s time. Sator digs it back up (immediately after burying it) and collects the gold.
It’s an appealing idea, but I don’t quite see how to make it agree with what we’ve been told about inverted physics. If there’s one consistent rule, it’s “what’s happened’s happened.” That gold’s timeline lies inside the buried capsule, not in Sator’s hands. By digging up the gold, Sator is changing the gold’s timeline. So where does that gold even come from? It has no sensible history, either forward or backward.
A similar problem exists with the detritus of the coming war that Dr. Barbara spoke of. When an inverted bomb explodes, how exactly are the pieces ending up in the drawers of Barbara’s lab? Or, viewed forward, who is going to collect all the bomb fragments and bring them together in place, so they can un-explode into an inverted bomb? I just don’t understand how this works.
(Now, what would work is if Sator took inverted and conventional gold out of a turnstile, and then buried the inverted gold in the capsule. From the gold’s perspective, the future buried it and then Sator dug it up and put it through the turnstile, turning it into regular gold. But that is clearly not what’s happening.)
Protagonist plans the Tallinn heist, and he specifically plans to keep the scheme out of the record so the future cannot learn what he did and tell Sator. But the plan doesn’t work because he doesn’t account for the notion of a temporal pincer movement. As the heist is kicking off, Sator starts his temporal pincer. He goes into a back room and orders Volkov to tell him everything as it happens.
The heist actually goes smoothly. As the heist is underway, we get to see that Neil’s car has a broken side mirror. That’s damage from the future. As Neil and Protagonist are speeding away with the 241, they ominously hear Sator talking on the radio backwards. Moments later they encounter an aggressive car driving backwards. It hits Neil’s side mirror, un-breaking it, and then turns around and follows them, still going backwards. (Again notice that the damage goes in the same direction as the person doing the damage.)
We later learn that this is a conventional car, driven by an inverted driver. We know that the driver is inverted because he is wearing a mask. We know that the car is conventional because Kat and Protagonist are able to operate the locks and brakes normally. (Moreover, if the car were inverted, it would have no reason actually to be there, since it ends up — starts, from its perspective — abandoned on the highway.) Driving a car oriented opposite from you would have to take enormous skill. For starters, the accelerator and brakes are effectively swapped, and your braking performance is limited by the car’s horsepower. That’s probably the driver’s only job. The car is able to go impressively fast in reverse, but if Christopher Nolan can acquire a car with its drivetrain turned around, I suppose so can Andrei Sator.
The enemy car pulls alongside and we see it contains Sator holding Kat at gunpoint. A moment later, a third, flipped car on the roadway un-flips and then drives, backwards, between Protagonist-Neil and Sator-Kat. We later learn that inverted-Protagonist is driving the car. We can also later determine that the car itself is also inverted, but that is much more subtle.
As forward-Protagonist looks at the third car, a look of recognition briefly crosses his face. I think he recognizes himself as the car’s driver. Protagonist throws the 241’s box across the third car’s hood to Sator. For a brief moment, you can see that the 241 is in his hand, not the case. Immediately after that, although we don’t see it at this time, Protagonist tosses the 241 into the third car. That makes no sense unless he recognizes himself.
Then Sator and his driver climb from their car into a fourth car (abandoning Kat), this one a conventional car driven conventionally. (From their perspective, they went the other direction.) So this car chase involved two conventional cars with forward drivers (one of them with inverted passengers), one conventional car with an inverted driver, and one inverted car with an inverted driver.
We don’t see it, but someone tosses the 241’s empty case on the side of the road. Meanwhile, Protagonist boards Kat’s car and applies the brakes. (During the process, “movie time” prevails, as it takes much longer to run out of highway than the few seconds it ought to take.) Neil calls the cavalry and Protagonist gets captured.
This is when it gets really interesting.
As Protagonist is taken into the Tallinn freeport, you see Sator pulling in Kat on the other side of a fence. (Sator is inverted, so from his perspective he is pushing her out.) Sator seems to be in a hurry; his driver is actually running. Protagonist is taken into a room with a turnstile, with the two sides separated by glass. There is a bloody bullet hole in the glass.
Sator interrogates Protagonist about the location of the 241. The interrogation is weird, because it only makes sense from Sator’s inverted perspective. There is a device reversing Sator’s words so Protagonist can understand them. It must be running inverted because we hear Sator say each line (reversed) after we hear the translation. Later, when we hear the interrogation from Sator’s point of view, Protagonist’s words come before the translation, so both sides of the translation are done by an inverted device, probably the same one.
During the interrogation, Sator shoots Kat. He counts down beforehand and up after, so you get the same countdown effect in both directions.
Kat getting shot is an important plot point, because it leads Protagonist and Neil to invert to try to save her. But there’s something very strange here. The inverted bullet wound nearly kills Kat. At the end, an inverted bullet kills Neil (a forward bullet, but Neil is inverted). And Dr. Barbara says an inverted bullet would be devastating.
But it’s been established that damage propagates in the direction of the person who does the damage. We see it with the bullet holes in the glass in this very scene. And it’s not just inanimate objects: when Protagonist stabs his inverted self, the damage goes forward. But this rule seems not to apply to bullet wounds in people! The damage Sator’s bullet does to the glass goes in Sator’s direction, but the damage it does to Kat goes in Kat’s direction. If I had to explain this, I guess I would say that actions that create a lot of entropy (i.e., bullets more than knives) encounter more resistance from the environment, and victims that create a lot of entropy of their own (i.e., people more than glass) resist more. We see later that resistance from the environment can turn an action around, and humans are indeed entropy machines. But I have no idea if this is what Nolan had in mind.
Forward-Sator now appears and questions Protagonist. Protagonist tells him that he already told inverted-Sator. (We find out shortly that he actually didn’t.) Ives arrives with Wheeler and the rest of the cavalry just as Sator is about to kill Protagonist. Sator flees into the turnstile and disappears.
After a moment our perspective shifts to Sator, emerging from the turnstile inverted. This is the first time the viewpoint is inverted. We see the interrogation again, and in this direction it makes sense. Then Sator grabs an air mask for himself and pushes Kat out the door. He has to hurry to get to the BMW (Neil’s car) after it arrives. We then return to Protagonist’s forward perspective. Neil has arrived and Protagonist learns that Neil has been part of Tenet all along. Ives explains the temporal pincer movement. Protagonist and Neil resolve to use the turnstile to save Kat, who has received a mortal wound from the inverted bullet. The bullet’s damage is mild compared to the radiation damage it does passing through a person, but that can be stabilized by spending enough time inverted.
Ives objects that they have controlled the turnstile for just minutes. Before that it belonged to Sator. They won’t be able to use it to turn forward again. Protagonist and Neil plan to use the Oslo turnstile a week earlier.
As they pass through the turnstile, we observe a color motif. The forward side of the room is lit by red light, while the inverted side is blue. The turnstile itself is neither. During the battle at the end, the forward team wears red patches and the inverted team wears blue patches. In fact, they don’t make a big deal about it, but Ives’s team now — which was a forward team until a moment ago — is wearing red patches. In the Making-of documentary, we learn that the red-blue motif is used even by the production team. When they plan the Oslo fight scene, forward characters are marked in red and inverted ones in blue.
Protagonist is considering going back outside. He worries about what happens if Sator follows thought on his threat to kill Kat in the past. Neil says “what’s happened’s happened.” Neil doesn’t want Protagonist to go because he worries, rightly as it turns out, that Protagonist will give Sator just what he wants. Inadvertently, though, he’s given Protagonist a reason to go back out, because Protagonist already saw himself out there.
Ives says “we can’t stay here.” We don’t know exactly how long they controlled the turnstile before they used it, but not very long. “Minutes” Ives said earlier. After that, Sator will come through the turnstile. In a way, this seems like an opportunity. They clearly have more force here that Sator will, so they have the opportunity to capture him. Maybe they are dedicated to the “what’s happened’s happened” principle, and they could see before that they weren’t there when Sator went through. Or maybe they are worried that Sator will kill himself if captured. Either way, they plan to clear out before he arrives.
Neil tells Ives to find them a shipping container that has just come from Oslo. They will ride it backwards, back to Oslo. It appears that they find an empty one, which is lucky. It also means we don’t have to wrestle with the question of what happens if they empty out and ride backwards in a container that was full going forward. Wheeler briefs Protagonist on what to expect when he goes out there. Most notably she tells him that if he encounters fire, ice will form on his clothes because the heat transfer is reversed.
Protagonist goes out and finds a car. Luckily, the car is inverted, so it’s not too hard for him to drive it. (It’s subtle, but we’re able to determine this later.) He follows the transponder to the case that originally held the 241. Once he finds it, he puts a bug in the box. Meanwhile, Sator searches the BMW for the 241 but comes up empty.
The 241 case flies back into the car from which it was thrown, bringing Protagonist’s bug with it. He hears Sator tell Volkov to bring the other sections of the algorithm to the hypocenter. That’s how Protagonist knows where to attack at the end.
The Protagonist gets in the middle of the car chase. The 241 has been in his car and we see it fly back to forward-Protagonist. A moment later, Sator tosses the 241 case across Protagonist’s hood to forward-Protagonist. The two Protagonists’ eyes meet for a brief moment. Sator swerves, hitting Protagonist’s car and flipping it.
Next we see Protagonist gasping, putting his mask back on. Sator is there, so this has to be a few minutes later (first he was in a couple of minutes of a car chase with forward-Protagonist and Neil). My guess is that Protagonist blacked out briefly. That means that you don’t suffocate immediately breathing inverted air; you just can’t breathe well. This tracks with the behavior of inverted oxygen in combustion that we’re about to discuss.
Sator taunts Protagonist for a moment, then drops a lighter to ignite gasoline leaking from the car. This sets off an explosion, ice forms on the car during the ensuing fire, and protagonist wakes up in a shipping container with Neil and Kat.
This sequence is quite subtle, but it all makes sense in light of some things that Neil explains shortly thereafter. Let’s take a closer look.
There are several facts we can establish: Our viewpoint is inverted; that’s the direction Protagonist is going, and plus we see cars going backward as the explosion takes place. The gasoline is inverted, because it burns away from the lighter rather than towards it. Ice forms on the car so the fire and the car are going in opposite directions. However, the ice is growing, not shrinking, so the car is going in the same direction as our viewpoint. Thus the car is inverted. (Also, it makes sense that an inverted car would run on inverted gas. An engine probably would not work well on inverted fuel.)
That means the fire that burns the car is going forward, even though the initial flame (setting off the spilled, inverted gasoline) is inverted. Somehow the combustion gets turned around. How does that happen? Here’s my theory, based on Neil’s subsequent remark and other aspects of inverted physics we’ve been able to observe.
The spilled gasoline burns to the car and sets off an explosion. Combustion takes heat, fuel, and oxygen. Heat is just molecular motion; it’s the same in either direction. The fuel is inverted. But the oxygen is forward. Whichever way the combustion goes, either the fuel or the oxygen is unhappy. We’ve already seen that objects can act opposite to their direction when forced to do so (recall the gold), and this provides another example . The explosion doesn’t really want to go backward with all that forward oxygen so it gets quashed by the environment. “Inverted explosion was pushing against the environment” as Neil explains in the next scene. And indeed the explosion looks like it gets cut off mid-explosion. (I’m curious how they filmed it.) But that explosion is sufficient to send gasoline everywhere, which is subsequently ignited by a stray spark from the forward environment. The resulting fire burns forward (backward from our perspective), pulling heat from the inverted car, and from Protagonist. He awakens in the shipping container, wearing thermal blankets and suffering from hypothermia.
Neil’s first words when Protagonist awakens are “You left Ives and his team a hell of a cleanup.” Indeed. By the time Protagonist’s car flipped, Sator has been in control of his turnstile for some time. So it’s impossible that Ives’s team is still inverted; they needed to turn forward again while they still controlled the turnstile. That means they had to save Protagonist going forward, probably before they took the Tallinn Freeport.
From Ives’s perspective, they had to take an unconscious Protagonist from the shipping container and put him into a flipped car. In fact they would have to take him from the shipping container before it was delivered to the Freeport (since they wouldn’t have access after it was delivered), which means they would have had to hold his unconscious body for a while.
In the container, Protagonist confronts Neil about his role in all this. Neil says he’ll tell him later. He does say that he doesn’t work for Priya. We learn at the end that that’s true; he works for Protagonist. Then Neil briefs Kat about inversion.
He begins by saying “every law of physics…” We don’t hear the rest of this, but what he’s saying is that every law of physics works the same forwards and backwards except for one, the Second Law of Thermodynamics, which says that entropy never decreases. Entropy is what gives us the so-called arrow of time. If the second Law could be reversed for some object — a fanciful notion outside this movie — it would be travelling backward in time.
Protagonist begins suffering the effects of the stab wound he’s going to receive. Neil explains what the algorithm is. In passing, he mentions the phenomenon that the environment pushes back against inverted actions. Neil and Protagonist discuss the grandfather paradox. Finally, the container arrives at the Oslo airport. Protagonist’s stab wound is pretty bad now. Protagonist, Neil, and Kat cross the tarmac to the Freeport doors. An imploding engine blows Protagonist through the door, into the fight with forward-Protagonist.
Stephen Ford has produced a video analyzing the fight:
I agree with most of it, but I’m not sure he’s right that punching an inverted antagonist is ineffective. From what we’ve learned about inverted physics, I think it probably is effective, creating bruises that go in the direction of the attacker. However, we have seen that the rules involving the interaction of objects going in opposite directions are not entirely clear, so he could be right.
In the course of the fight, Protagonist gets un-stabbed. He fires the gun, not to try to shoot his forward self, but in an attempt to empty the gun.
He goes through the turnstile and Neil gives chase. Neil catches him and pulls off his mask, but when he recognizes Protagonist, he throws back the mask and runs back to save inverted-Protagonist from the younger Protagonist.
On Protagonist’s way out, you briefly catch a glimpse of his fight with himself. At that moment there are three Protagonists running around the Freeport.
Protagonist, now forward, runs out the door and yells “go!” to Neil. This is earlier than he entered, since he certainly got out faster than he got in. From the inverted perspective, it’s after he entered. Immediately after he exits, we see the exit again backward, from Neil’s perspective. Protagonist yells “og!”
Neil takes Kat in. They pass through the halide gas, but with their own air it’s not a problem. It’s around now that forward-Neil senses their presence. Then Neil sees forward Neil and Protagonist stumble in reverse back into the halide gas. Neil takes Kat through the turnstile without further complication.
Interleaved with this, we also watch Protagonist acquire an ambulance. But the two threads are not simultaneous. From the point Protagonist emerged from the Freeport, he is moving forward but Neil and Kat are moving backwards. So Neil and Kat must emerge from the Freeport much earlier than Protagonist obtains the ambulance. We don’t see it, but they must cool their heels on the tarmac a few minutes waiting for him.
The three make good their escape. Protagonist meets Priya again and learns some backstory. Priya sends them to the Magne Viking, where Tenet has a turnstile. When we see them next, they have inverted again. We didn’t see them arrive, but they are still in the North Sea, so it hasn’t been long.
On the Magne Viking we learn that Sator’s fitness tracker that he’s always checking is a dead man’s switch. (It’s not clear where they learned this information.) When he dies, it will send out a signal to activate the algorithm and destroy the world. Kat reveals that Sator is dying and intends to take his own life, to take the world with him. They deduce that he will go back to the family holiday in Vietnam to commit suicide.
Protagonist connects his information that the algorithm is going to the hypocenter with Sir Michael’s earlier remark about a detonation in Stalsk-12 to deduce that that’s where and when the algorithm is going. That detonation, the Sator family holiday, and the opera siege that opened the movie were all at the same time.
They plan to go back to that date. Kat’s job is to go back to Sator’s yacht and stall his suicide. Tenet’s assault force, together with Protagonist and Neil, will seize the algorithm. If they can seize it without alerting Sator, he will suicide as planned without destroying the world.
Protagonist tells Ives that Stalsk-12 is their destination. Now the ship itself isn’t inverted (various visual cues are running backward from Protagonist), so it’s not just a matter of telling the captain to sail there. The ship must have already come from there. A message needs to be sent to the captain far enough back that he can sail to the Arctic Ocean from wherever the ship was before that, at the right time for the attack, and then continue on to the North Sea where they are now.
Protagonist gives Kat a phone that she can call if she feels threatened. Her message will go into a voicemail, and someone in the future (probably himself since at this point he doesn’t know about the resources he’ll have later) will send the information back to Protagonist so he can act on it.
This brings us to the climactic battle.
The Tenet force flies into Siberia. It is broken into red and blue teams, the former attacking forward and the latter backward (again following the red-blue motif). Both teams attack at the same time, but the blue team is first in the sense that the blue team passes information on to the red team.
Sator is setting off a bomb at the hypocenter to seal the algorithm underground. Tenet’s plan is to fail to defuse the bomb, creating a diversion that allows Protagonist and Ives to seize the algorithm undetected. Things do not go as planned.
In the battle there are four threads going simultaneously: red team, blue team, Kat and Sator, and Neil, who starts with blue team but peels off on his own mission. (There’s actually a fifth thread — another Neil — but we don’t get to see that one. We’ll return to that.) The red-team action and blue-team action are awfully similar, so there’s an audio cue whenever the blue team is on screen to help distinguish them.
The red team is carried to and from Stalsk-12 in helicopters, while the blue team is carried in shipping containers (blue, of course) hauled by helicopters. Going forward, the red team arrives at the outskirts of town, while blue team is evacuating from the same location. The blue team starts reverse-embarking right away, so some of them just made it.
Going backward, the teams arrive/depart from the other end of town, above the hypocenter. The blue team, led by Wheeler, is arriving just as the bomb goes off. Wheeler announces they are coming in on a Shockwave. Inverted, the Shockwave is pulling them in.
As the blue team is arriving and the bomb is unexploding, we see Neil’s truck back toward the hypocenter with a cable into the hole.
The ten-minute battle alternates between the various teams, told in each team’s internal chronology. Thus at the beginning of the scene we see red team at the beginning of the battle and blue team at the end. By the end of the scene it’s reversed. The two directions converge at the five-minute mark, with the spectactuar sequence where a building is blown up in both directions.
Protagonist and Neil use the building’s destruction as a diversion to enter the tunnel that leads to the hypocenter without being seen. But just as they enter, a truck comes driving at them, honking its horn. Naturally they don’t stop for a presumably hostile truck, but we later learn that Neil is the driver.
A moment after they enter the tunnel, a trap is triggered, collapsing the tunnel and barely missing them. The tunnel is not actually blocked though; you can see daylight on the rubble. In fact the tunnel does not go immediately into the hillside. There’s a long concrete extension out from the hillside and that’s the part where the trap goes off. When Protagonist remarks that they are committed now, I think he means that one can’t get out that way quickly without a ladder or a rope.
Next (from the viewer’s viewpoint) we see Neil, inverted, watching the same tunnel. An inverted minute has elapsed so it’s a little earlier. Neil watches Volkov un-set the trap, and then un-rappel into a hovering helicopter, which flies away in reverse. (Protagonist noticed the helicopter earlier in the scene, going forward.)
At this point Neil sets off on his own, and heads to the Stalsk-12 turnstile to invert back to forward. I do not understand why he does this. It seems that he wants to warn his friend about the trap, but the easiest way to do that is to take advantage of the temporal pincer movement and notify red team afterward. For whatever reason, Neil instead goes with the much-riskier plan of using an enemy turnstile during a battle.
It actually goes smoothly though. Perhaps it never occurred to the enemy to guard against such an audacious move. Neil waits until some enemy troops have inverted and then inverts himself. While he waits he sees himself hurrying out of the turnstile ahead of the enemy, illustrating the last-in, first-out nature of a turnstile.
Neil, now going forward, grabs an unattended truck and heads back to the tunnel, but he arrives just too late to warn Protagonist and Ives. He then decides to take his truck up above the hypocenter. Along the way, we get to see the forward version of a truck sequence we saw inverted earlier. In the earlier scene we saw Neil nearly get hit by a truck, and then fire on the truck. We now see that he was firing on himself.
While we’re watching all this, Protagonist and Ives are at the hypocenter, stuck behind a locked gate. On the other side of the gate is a dead man in a Tenet uniform. He has the trinket that identifies him as the one who saved Protagonist at the beginning, who we soon learn is Neil. Let’s call him Neil 2, to distinguish him from the slightly younger Neil who is currently headed up top with a truck.
On the other side of the gate is Volkov, who is prepping the algorithm. Volkov knocks out Ives with a bullet to his helmet, and disarms Protagonist. Sator, on the phone from his yacht, gives his evil villain speech, which burns a lot of time while Neil does his thing and Wheeler fights to the extraction point.
When Sator grows bored of posturing, he tells Volkov to kill Protagonist. Volkov approaches Protagonist but just as he pulls the trigger, Neil 2 revives and takes the bullet. Neil 2 is inverted, and, as usual for bullet wounds, the wound went in his direction rather than the shooter’s. Neil 2 opens the gate. From his perspective, he does so by locking it, just before taking the bullet that kills him. Neil is indeed an expert locksmith if he is able to lock an inverted lock quickly.
Volkov is startled by the dead man coming to life, but Protagonist is not. He charges through the gate, grabs a gun and shoots Volkov twice. Then out of bullets, he closes with Volkov and fights him hand-to-hand. All this time Neil 2 is working on unlocking the gate. Ives comes to and steps through the gate.
Neil 2, from our perspective, finishes unlocking the gate and heads back up the tunnel. For a while it puzzled me where he could be going (coming from), since the tunnel is blocked. But, as we noted earlier, you can see daylight on the rubble. The tunnel is not blocked to an inverted person who can jump down into the tunnel. To arrive in time to help, Neil 2 must have come in on the shockwave with blue team and immediately hurried to the tunnel and on to the hypocenter.
Protagonist defeats Volkov and tosses him down the pit. He and Ives start wrangling the algorithm. Neil arrives above the hypocenter. Kat fails at her one job and kills Sator. At that moment, Protagonist and Ives have just disconnected the algorithm so it doesn’t activate. Neil throws a cable down the hole. Protagonist and Ives grab ahold. Wheeler is the last one out on blue team. Neil hauls Protagonist and Ives to safety as the bomb goes off.
Kat dives off the yacht as her younger self watches. Mahir picks her up and also drags away Sator’s body.
Protagonist, Neil, and Ives meet up. Ives gets the drop on Protagonist, but decides not to kill him and splits up the algorithm instead. (Earlier he had said that no one who has seen the algorithm can leave the field, because it’s essential that the future not learn its location.) Why they can’t simply destroy the algorithm is never explained.
Neil decides to go back into the battle because he’s the only locksmith good enough to have gotten the door open in time. As he turns we see the trinket and learn that Neil is going to his death.
I think Neil knows it too. He knows the tunnel is blocked, and he knows he doesn’t get out the way that Protagonist and Ives do. The only way he can get out inverted is to wait until before Protagonist and Ives set off the trap. If he did that, it would look like he was entering (running backward) with Protagonist and Ives. But he was watching at that time and knows he didn’t do that. So he knows that the only way he survives is if he waited so he could reverse-exit before Protagonist and Ives entered. But that would mean doing it without the benefit of a diversion, which would compromise the mission. Neil wouldn’t do that. In any case, whatever suspicions he has, Protagonist’s attitude confirms them.
As he leaves, Neil reveals that he has been living backwards, he and Protagonist have been friends for years, and Protagonist recruited him. He also reveals that Protagonist is in charge of the operation.
In an epilogue, Priya is about to have Kat killed. Kat uses the phone Protagonist gave her to call for help. Protagonist shows up and kills Priya instead. It’s not clear when in his lifeline this is, but it can’t be too much later, because he doesn’t appear to have aged much. Whenever it is, he says he realized that he’s been working for himself all along, confirming what Neil just told him.
The penultimate scene ended with a big teaser for a sequel/prequel. Neil tells Protagonist that the whole operation is Protagonist’s temporal pincer movement and he’s only halfway there. “You’re gonna love it!” I very much hope that happens. I think Nolan has only scratched the surface of what he can do with this premise.