Opening title card explaining the Deviants and Eternals - the Deviants were created by the Celestials to hunt predators that prey on intelligent life on newly evolving worlds, but then they started to hunt the life as well, so Ceestials created the Eternals to kill the Deviants.
Opens 5000 years ago in Mesopotamia a man is fishing on some rocks with his son (?) and is attacked by a Deviant from the ocean. The Eternals show up and a short battle commences, after which they line up in a triangular "hero" pose and this rolls into the Marvel logo opening.
Jumps to present day - Sersi (Gemma Chan) and Dane Whitman (Kit Harrington) are teachers in the UK and dating. During a class lesson, a large earthquake strikes, and Sersi saves a child from a falling object by turning it to sand. Later while out on a date, a Deviant attacks Sersi, Sprite (Lia McHugh), and Dane; during the battle Ikaris (Richard Madden) shows up and they fight it off after noting that they thought all the Deviants were destroyed and unlike others, the Deviant was able to heal its wounds.
The group decide to visit Ajak (Salma Hayek) as she was the leader of the group. After arriving at the midwest ranch where she is now living, they discover her dead body, A small golden device leaves Ajak's body and enters Sersi ( this is how she communicated with the Celestials) - they then decide to round up the rest of the Eternals to deal with the Deviants.
Thena (Angelina Jolie) and Gilgamesh (Don Lee) are in Australia (I think) due to an issue with her memory causing her to randomly attack the other Eternals. Gilgamesh is obviously in love with Thena but it is not played as a romantic relationship.
Phastos (Brian Tyree Henry) and his husband live with their child and he decides to help due to the fact that he has fully embraced the human race and wants to protect his family.
Makkari (Lauren Ridloff) has been living in the Eternals ship all this time (I guess, since there is a bunch of food containers and mess strewn about.
Kingo (Kumail Nanjiani) is a Bollywood actor ( there is a short dance routine that introduces this) and comes with the group along with his valet (don't recall the name) who tries to document everything on video.
Druig (Barry Keoghan) is living in some rainforest controlling a small village of people after losing faith in humanity and wanting to control them to stop war, famine, etc. Gilgamesh is killed fighting the Deviants in the forest.
Sersi learns that the Celestials created both races and that the Eternals are basically just very advanced robots. They seed young planets with a Celestial "egg" that takes eons to mature. The evolving intelligent life on these planets feeds the Celestial's growth, so the Eternals are sent to protect the evolving life forms and kill the Deviants. After the emergence, the Eternals are " rebooted" and sent to another world (this is the cause of Thena's memory issue, as she knows that the planet is doomed) - this cycle has gone on for millions of years. Earth was seeded and Tiamut is about to emerge (this was the cause of the earthquake earlier). Once awakened, the entire planet and all life will be destroyed.
They debate on what to do and some decide to try and find a way to stop the emergence. Ikaris disagrees, Sprite and Kingo are on his side but Kingo agrees to help.
Phastos designs a device (Uni-Mind) that will allow Druig to channel all the Eternals energies in the hope of controlling Tiamut and putting him back to sleep.
Sersi learns that Ikaris knew about the Celestials actual plans and this is why he left the group hundreds of years ago. He killed Ajak because she had decided to help stop the emergence and save Earth.
The group go to where Tiamut is and attempt to use the device - Ikaris and Sprite attempt to stop them. Sersi then uses the device to amplify her power and turn Tiamut to marble just as his hand and part of his head is emerging from the Indian Ocean.
Ikaris flies off into space (towards the sun - unclear if he just left or flew into the sun and killed himself), then Sersi makes Sprite a real human with what remains of her power.
A few days (?) later Thena, Makkari, and Druig leave in the ship to seek out other Eternals and try and stop the cycle of destruction. Sersi, Kingo, and Phastos stay on Earth but are then pulled into space by Arishem and vanish.
The two end credit stingers: 1) Dane is looking at an old box and pulls out a sword that is wrapped up. Just as he is about to touch it, an off screen voice stops him. 2) On the Eternals' ship, Pip the Troll appears and introduces Starfox.
