The full story
The Eternals have been on Earth since the dawn of human civilization, guiding and protecting from the shadows. They are not gods, though humans have worshipped them as such. They are synthetic beings created by the Celestials—cosmic entities who seed life across the universe. Their mission was to kill Deviants, the predatory creatures that threatened early humanity.
The Deviants are gone. The Eternals scattered centuries ago, living among humans, forbidden to interfere in their conflicts. Sersi teaches in London. Sprite stays eternally childlike and resents it. Kingo became a Bollywood dynasty, playing his own "descendants" for generations. Druig runs a compound in the Amazon, secretly using mind control to create peace. Thena struggles with a degenerative memory condition. Gilgamesh cares for her in Australia. Phastos gave up on humanity after Hiroshima. Makkari waits in the Eternals' ship, the Domo. Ikaris left Sersi without explanation.
Then Deviants return, evolved and intelligent. They kill Ajak, the Eternals' leader, and Sersi inherits her ability to communicate with the Celestials. What she learns is catastrophic.
The Celestials do not seed life out of benevolence. They plant Celestial embryos in planets, using intelligent life as energy for the birth. Earth has been an incubator for millions of years. The Emergence—the birth of the Celestial Tiamut—is days away and will destroy the planet and everyone on it.
The Eternals were not protectors but gardeners, ensuring enough humans survived to power the Emergence. Every civilization they nurtured, every life they saved, was to feed a Celestial. Their memories have been wiped and reset countless times across countless worlds.
Ikaris knew. He has been loyal to Arishem, the Prime Celestial, all along. He killed Ajak when she decided to stop the Emergence. He believes the birth of a Celestial justifies any cost—including Earth and Sersi.
The Eternals split. Ikaris and Sprite side with Arishem's plan for the Emergence. Kingo, unwilling to fight his family on either side, leaves before the battle begins. The final battle occurs as Tiamut begins to emerge from the Earth's core.
Sersi, amplified by the other Eternals forming the Uni-Mind, turns Tiamut to marble before it can fully emerge. The Celestial dies mid-birth, its hand and head frozen in stone, rising from the ocean. Earth is saved.
Ikaris, unable to live with his betrayal, flies into the sun. Sprite becomes human, finally able to age and live a mortal life. The remaining Eternals split—some staying on Earth, others leaving to find more Eternals and tell them the truth about their mission.
The mid-credits scene introduces Thanos's brother Starfox and Pip the Troll. The post-credits scene shows Dane Whitman, Sersi's human boyfriend, about to claim the Ebony Blade, interrupted by an off-screen voice (Blade).
The half-emerged Celestial is now part of Earth's geography. The Celestials know what the Eternals did.