NOTE: This spoiler was submitted by Jeremy

The film opens at an opera house in Kiev. Just as the performance is about to commence, Ukrainian gunmen storm the place, shooting the conductor and terrorizing the orchestra and patrons. Outside the building, an undercover SWAT team prepares to head in. They gas the place to put the patrons and performers to sleep as they head in to rescue a compromised spy (Jefferson Hall) and recover an unknown artifact. A man known only as “The Protagonist” (John David Washington) identifies the spy with the phrase “We live in a twilight world,” to which the man replies “And there are no friends at dusk.” After the spy is recovered, the team handles the gunmen’s bombs. The Protagonist goes down to recover the bombs and sees a bullet hole. An unknown agent with a red tag on his bag steps in and appears to take the bullet as it flies backwards from where it was shot. The agents then throw the bombs into the nosebleeds where there are no patrons as it explodes. As the agents are getting away, The Protagonist is captured.

The man wakes up between two train tracks as his captors have him and another agent tied up, attempting to torture them for information. The Protagonist tries to take a cyanide pill, but one of the captors takes it from him. The other agent on the ground takes his out, and The Protagonist jumps for it and takes it, seemingly dying. He later awakens in a hospital, as this was just a test, meaning that the pill was fake, but all his colleagues are dead. His boss Victor (Martin Donovan) recruits him for a new mission under an organization called Tenet, as this new job concerns the fate of the world.

The Protagonist is taken to meet a woman named Laura (Clemence Poesy), who is set to show him how things pertaining to the mission work out. She gives him a gun with an empty magazine and has him aim it at a rock. The bullet in the rock flies back into the gun. Laura explains that the entropy of the bullets is inverted, which means they pass backwards through time. Through more tests, The Protagonist sees that he can catch or move the inverted bullets in the right position. The people in charge have gathered more inverted items, and the plan is to locate the source of the inverted bullets before the creators can use their technology to pass things like nuclear weapons through inversion.

The Protagonist tracks the bullets to a man named Sanjay Singh (Denzil Smith). He calls Victor to ask for assistance in infiltrating Sanjay’s home. The Protagonist is met by a local man named Neil (Robert Pattinson), who was sent to help. The two use bungee cords later that night to make it up into Sanjay’s building, but as they try to interrogate him, they find that the one to speak to is Sanjay’s wife, Priya (Dimple Kapadia), who works for Tenet. She speaks to The Protagonist and says the bullets come from a Russian oligarch named Andrei Sator (Kenneth Branagh), who can apparently communicate with the future. Priya tells The Protagonist to get close to Andrei and find out how he produces the inverted bullets.

The Protagonist meets with Sir Michael Crosby (Michael Caine) in a restaurant. Crosby tells him about how Andrei grew up in a Soviet “secret city” that endured a major accident, and it was later used for underground testing. Andrei came out from there and built a fortune before staying in England and marrying a woman named Katherine Barton (Elizabeth Debicki), with whom he is now estranged. Crosby suggests he get close to Andrei through Kat, and he gives The Protagonist a fake Goya painting that is one of two, the other one having been bought by Andrei.

After observing Kat with her son Max (Laurie Shepherd), The Protagonist meets her and learns that Andrei is blackmailing her by threatening to expose her part in the fraud with the painting. The last time they were happy was on his yacht in Vietnam, but he offered her a chance to leave, on the condition that she never see Max again. Kat reacted in rage and left with Max, and as she got away, she observed a woman diving off the yacht. Moments later, some of Andrei’s henchmen arrive to escort Kat out. A few stay in the kitchen as The Protagonist tries to follow her, and he fights them off. Kat even sees this as one henchman falls through the door before she is driven away.

Kat calls The Protagonist back and tries to have him steal the painting back. He works with Neil and a fixer named Mahir (Himesh Patel) to break into Andrei’s storage facility at Oslo Airport. After Neil gathers intel on the place, he determines that the security is going to be very tight, so he plans to crash a plane into the hangar as a distraction. Together with a crew, the team enacts their plan as The Protagonist and Neil enter the facility under professional guises. The cargo jet containing a ton of gold bars crashes, and the two head on to a room where they find a room separated between a glass window with a machine on both ends. The window has bullet holes that The Protagonist says come from an event that hasn’t happened yet. The machine opens, and two identical men (“antagonists”) emerge. The one on Neil’s side runs past him, but the other one, who is inverted, appears to struggle with The Protagonist. The antagonist reaches for an inverted gun, which catch the bullets from the holes. Neil returns after unmasking the other antagonist, but he stops The Protagonist from killing the other man, just as he appears to fly out the loading door. They then position themselves safely before a recovery team enters the facility.

The Protagonist meets with Priya on a boat, where he learns that the machine is called a Turnstile, which is what inverts time and was made in the future. She also reminds him not to kill Andrei before they know what connection he has with the future.

Kat is told that the painting was destroyed, and she later sets up a meeting with Andrei. The Protagonist joins them and others for a dinner, where Andrei appears to try and threaten The Protagonist over his supposed involvement with Kat, since he has seen them together. However, The Protagonist manages to get Andrei to set up a boating trip for the next morning to discuss the opera.

Before Kat and Andrei head to meet The Protagonist, he tells her that “instinct” told him to move the painting before the crash. They meet with him and have a brief discussion before Kat tries to drown Andrei by loosening his harness. The Protagonist then turns the boat around to rescue Andrei. Kat chastises him for it, as well as for lying to him about the painting. Andrei then asks to meet with The Protagonist for repayment, and he asks not only for him to not retaliate against Kat, but also to help acquire a case of plutonium that Andrei has his eyes on. Andrei recounts digging plutonium out of his hometown and killing a co-worker to prevent anyone else from securing better opportunities. He goes to his room with Kat and threatens her, explicitly stating that if he cannot have her, nobody can.

Andrei then goes outside as a helicopter comes down with a crate containing gold bars. The Protagonist observes as Andrei beats another man to death with a gold bar. He is spotted and grabbed by Andrei’s henchmen, and he attempts to out The Protagonist as a spy with the “twilight world” phrase, but he doesn’t budge. He then lets The Protagonist go and agrees to help with getting the plutonium from Tallinn.

The Protagonist reconvenes with Neil to enact the heist. Meanwhile, Kat and Andrei have another heated confrontation over her attempt to kill him, as she now has a gun aimed at him. He beats her and then takes her as a hostage. The Protagonist and Neil follow a truck and have their team use other vehicles ty surround the truck, allowing The Protagonist to make his way in and grab the plutonium case, only to see that the item is not plutonium, but a different artifact entirely. Andrei’s van drives up near them as he shows them he is aiming a gun at Kat’s head. An inverted car that previously appeared to crash passes between them driving in reverse, and The Protagonist appears to toss the case to Andrei. He then tries to make his way to the other car as Andrei switches cars so that he can save Kat. After the vehicles stop, Andrei’s men shoot at The Protagonist and Neil.

The Protagonist is captured and brought to a separated room like the one at the Oslo facility. Andrei has Kat while they are inverted, and he demands to know where the plutonium is, even going as far as to wound Kat in the abdomen with an inverted bullet. The Protagonist tells him the plutonium is in the glove box of the inverted BMW. After Andrei leaves, other Tenet agents led by Neil and Agent Ives (Aaron Taylor-Johnson) come in to kill his men. They get The Protagonist and Kat to safety, but she is dying from the bullet wound. The Protagonist becomes suspicious of Neil after learning he was always involved with Tenet, thinking he led Andrei to know more than he lets on. He reveals he lied about the location of the artifact.

The Protagonist tries to save Kat by bringing her through the Turnstile to take them through the previous week. He enters through the machine with a respiratory mask (inverted lungs won’t support normal air and vice versa) and drives to the moment of the chase, where he ends up in the BMW that crashes. After Andrei sees that what he wants isn’t there, the car explodes, but the inversion causes The Protagonist to almost freeze. After he is recovered, he and Neil go through with taking Kat through the Turnstile to go to the week before to the Oslo facility. The Protagonist enters, revealing himself as the “antagonists”. He fights his inverted self while Neil had seen that the person he was chasing was The Protagonist. He then un-inverts himself, and Kat is okay.

The Protagonist meets with Priya again, where he learns this time that the artifacts that Andrei was looking for are meant to make up a device called an Algorithm, which he may use to invert the entire world. Future humans are said to be using the Algorithm to reverse the effects of global warming. Priya tells The Protagonist that is not the ONLY Protagonist that is capable of saving the world, but he believes he is. When he suggests that they continue using Kat to get close to Andrei and stop him from using the Algorithm, Priya arranges for the two to meet on a ship.

Kat tells The Protagonist that Andrei is secretly dying from pancreatic cancer, and his plan is to use the Algorithm to kill himself at the right moment, inverting humanity and wiping them all out using the same “if I can’t have you” reasoning. She suspects that he will commit the act on the day they were on their yacht in Vietnam.

The Protagonist and Neil meet with Ives and his team as they head to the location of the dead drop where the Algorithm is assembled and will be set off, which is in the secret city Andrei came from. Ives instructs his team to go through a temporary pincer movement, which will see half of them moving normal, and the other half moving inverted to get through the zone. Meanwhile, Kat inverts herself to go back to the day on the yacht to delay Andrei from killing himself. As the Tenet agents run through the zone, coming across numerous explosions. The Protagonist heads into the drop zone with Neil’s help, as well as a masked agent with a red tag similar to the agent at the opera house, but they are prevented from reaching the Algorithm because of a gate. He appears to take a gunshot from a henchman, but since he is inverted, he helps The Protagonist make it through the gate to retrieve the Algorithm. After the plan succeeds, Kat decides she cannot stand to watch Andrei die happy thinking he won, so she drops sunscreen and water on the deck before shooting Andrei in the chest. She then uses the greased up floor to push his body off the yacht, where he hits the railing on the way down. Kat then jumps from the yacht, revealing that her past self witnessed her own self jumping. She goes to meet with Mahir.

The Protagonist, Neil, and Ives disassemble the Algorithm, and Ives orders the two to stay hidden or he will have to kill them. As Neil and Ives walk away, The Protagonist notices the red tag in Neil’s bag, meaning he was the one who got shot near the gate, AND all the way back to the opera house mission. He bids The Protagonist farewell, revealing that it was he all along who recruited Neil for Tenet in the future, and this is the end of a friendship that The Protagonist hasn’t encountered yet.

In London, Priya and one of her gunmen watch Kat as she goes to pick up Max from school. Before they can move in on her, The Protagonist kills the gunman and sits behind Priya in her car. He tells her that is will go on to be the founder of Tenet, and that they were both working for him all along. Since she is a loose end, The Protagonist kills Priya. He then watches Kat leave with Max.

Brought to you by

Tenet is an organization from the future that handles threats of terrorism. They learn of a machine called a Turnstile that can invert time, having been set up by Russian oligarch Andrei Sator. An agent known only as The Protagonist is recruited by Tenet to find out where inverted items are coming from, leading him to arms dealer Priya Singh. She tells him about Andrei and has him use Andrei's estranged wife Kat Barton to get close to the man and find out what his plan is. Kat is trapped in an abusive marriage, as Andrei tries to control her and keep her away from their son Max. The Protagonist works with a man named Neil in the mission.

After a heist where The Protagonist and Neil help Andrei acquire what they believe is plutonium, Andrei mortally wounds Kat when he doesn't immediately get his artifact. After Neil reveals his work with Tenet, he helps The Protagonist use the Turnstile to invert time to save Kat.

The Protagonist learns that Andrei wants to assemble a device called an Algorithm, which future generations will use to reverse the effects of global warming. Kat tells The Protagonist and Neil that Andrei has terminal pancreatic cancer, and he plans to use the Algorithm to invert the world and have humanity die with him. They, along with Tenet agents, trace the location of the Algorithm's detonation zone to an abandoned Soviet city. The Protagonist manages to find and acquire the Algorithm, while Kat inverts herself to the last happy day she had with Andrei, which is when she figures he will kill himself to invert humanity. After the plan succeeds, Kat kills Andrei early before he can think he has died happy and successful in his plan.

The Protagonist parts ways with Neil, who, as it turns out, was recruited by The Protagonist in the future to join Tenet, and he has already helped The Protagonist throughout his journey since he has been on an ongoing mission from the future that has led to the end of his friendship with The Protagonist, which is something he will soon experience.

The Protagonist arrives in London to find Priya trying to kill Kat, but he informs her that he will go on to be the founder of Tenet, and he kills her, allowing Kat and Max to be free.