The Protagonist's History
A CIA agent, the "Protagonist", participates in an extraction operation at a Kyiv opera house. A masked soldier wearing a red trinket saves his life by "un-firing" a bullet through a gunman. After seizing an artifact, the Protagonist is captured by mercenaries. He is tortured and consumes cyanide. He awakens to learn the cyanide was a test of loyalty; his team has been killed and the artifact lost.
The Protagonist is recruited by an organization called Tenet. A scientist briefs him on bullets with "inverted" entropy, meaning they move backward through time. She believes they are manufactured in the future, and other inverted objects seem to be remnants of a war in the future. The Protagonist meets Neil through a CIA contact, and they trace the inverted bullets to arms dealer Priya Singh in Mumbai. They learn that Priya is a member of Tenet, and her cartridges were purchased and inverted by Russian oligarch Andrei Sator.
In London, the Protagonist approaches Sator's estranged wife Kat, an art appraiser who falsely authenticated a forged Goya drawing. She tells him that Sator purchased the drawing from the forger, Arepo, and is using Kat's authentication as blackmail to control her in their relationship. The Protagonist and Neil plot to steal the drawing from a freeport storage facility at the Oslo Airport. There they fend off two masked men who seemingly emerge from a strange device. Afterward, Priya explains that the device is a turnstile, a machine that can invert the entropy of objects and people, and that the masked men were the same person traveling in opposite directions through time.
On the Amalfi Coast, Italy, Kat introduces the Protagonist to Sator, and learns the drawing is intact. Sator plans to kill the Protagonist, but the Protagonist saves Sator's life after Kat attempts to drown him. Sator and the Protagonist strike a partnership to retrieve a case that supposedly contains plutonium-241. In Tallinn, the Protagonist and Neil ambush a convoy and steal the case, which actually contains the artifact lost in Kyiv. They are ambushed by an inverted Sator holding Kat hostage. The Protagonist gives an empty case to Sator, who retreats after receiving it. The Protagonist rescues Kat but is soon captured and taken to a warehouse with a turnstile.
In the warehouse, the inverted Sator shoots Kat with an inverted round, while the non-inverted Sator demands the location of the artifact. Tenet operatives led by Ives arrive and rescue the Protagonist, and Sator escapes into the turnstile. The group takes Kat through the turnstile, inverting them and reversing Kat's bullet wound. The now-inverted Protagonist travels back in time to the ambush site, where he attempts to retrieve the artifact but is intercepted by Sator. The Protagonist's car is overturned and catches fire, but Neil saves him and reveals he is a member of Tenet.
The Protagonist, Neil, and Kat travel back in time to the freeport in Oslo. The Protagonist fights his past self, enters the turnstile, and reverts, followed by Neil and Kat. Later, Priya explains that Sator is collecting the artifacts to assemble an "algorithm" which is capable of catastrophically inverting the entropy of the Earth.
Kat reveals Sator is dying from pancreatic cancer. They learn that Sator is using a dead man's switch to trigger the algorithm. Kat believes Sator will travel back in time to commit suicide during their vacation in Vietnam, so that the world will die with him at the last moment he was happy. The Protagonist, Neil, Kat, and Tenet troops travel back in time to that day, where Kat disguises herself as her past self to keep Sator alive long enough for Tenet to secure the algorithm. Tenet tracks the algorithm to Sator's hometown in Northern Siberia, where it is heavily guarded. They launch a "temporal pincer movement", with non-inverted red team troops and inverted blue team troops making a simultaneous assault. At a critical moment, an inverted blue-team soldier wearing a red trinket sacrifices himself to save the Protagonist and Ives. Meanwhile, in Vietnam, Kat kills Sator just as the Protagonist secures the algorithm.
The Protagonist, Neil, and Ives break up the algorithm and part ways. The Protagonist notices that Neil is wearing the red trinket. Neil reveals he was recruited by the Protagonist in the future and this mission is, from his perspective, the end of a long friendship. Since she knows too much, Priya attempts to have Kat assassinated, but she is killed by the Protagonist, who realizes he is the mastermind behind Tenet.
