No doubt that 'Tenet' will endear itself to some of Christopher Nolan's most staunchest fans, but for the rest of us mere mortals, the ending of 'Tenet' was just as confusing and oblique as the rest of the movie.
What exactly was the 'algorithm' that the organisation Tenet were trying to find? How did Sator communicate with the future? Was Robert Pattinson in the opening scene at the opera? Was Robert Pattinson's character actually from the future? Why was the sound so bad throughout the movie?
We've covered the last part in another piece, but for now, we'll try to make some sense of the ending. So, let's go through the final battle sequence and how the 'algorithm' factors into it. The 'algorithm' is a doomsday device that would basically invert the world and destroy all existence. Andrei Sator, Kenneth Branagh's character, built the algorithm with the help of unknown people in the future. Global warming has adversely impacted the people of the future and, as revenge for this, they plan to destroy our present.
Sator's plan was to start the 'algorithm' and destroy the world along with himself because, as he told Kat - Elizabeth Debicki's character - numerous times that if he can't have her, nobody else can. The 'algorithm' is activated by his heartbeat through a dead-man switch. If he dies, the 'algorithm' is activated and the world is completely inverted, thus destroying all life as we know it. The organisation known as Tenet tracked all the pieces of the 'algorithm' to a closed city in the former Soviet Union known as Stalsk-12. The city is important because it's where Sator first learned of time inversion and the people from the future made contact with him.
The "temporal pincer movement" sees half the team moving forward in time with the other half moving backward in time. The idea is that the team moving backward in time can feed the information back to the team moving forward through time, thus ensuring their success. The 'algorithm' is successfully pulled out of the mine before it explodes, only for us to realise that Robert Pattinson's character was also at the very start of the movie as the person in the black uniform and ventilator who saved John David Washington's life.
The three characters, Ives, Neil, and the Protagonist, split the 'algorithm' into three pieces and take the pieces with them, but it's only then that it's revealed that Neil is actually from the far future and that John David Washington's character recruited him there. They have, in fact, been friends for years. Not only that, when we cut to the final moment where John David Washington's character kills Dimple Kapadia's character, Priya, in London, he realises that it was he himself who created Tenet and started everything in motion, hence why the clunky final line - "I'm the Protagonist."
Ultimately, the confusing ending is just one of several problems with 'Tenet'. Normally, when we do these kind of features about movie endings, it's done more to talk about it in a general sense and maybe link it back to themes or scenes earlier in the movie. Sometimes it's even just to gush about how good they are.
For this, however, it's basically an explainer - and a necessary one at that.