In the beginning, the Celestials created the sun and other forms of life, but monstrous creatures known as Deviants began to run rampant. The leader of the Celestials, Arishem (David Kaye), brought forth an immortal group of superhumans known as the Eternals from the planet Olympia and sent them on their ship, the Domo, to Earth.
The Eternals awaken, with Arishem choosing Ajak (Salma Hayek) to lead them. Ikaris (Richard Madden) meets Sersi (Gemma Chan) as she sees Earth for the first time and says it’s beautiful. They are joined by Thena (Angelina Jolie), Kingo (Kumail Nanjiani), Phastos (Brian Tyree Henry), Druig (Barry Keoghan), Sprite (Lia McHugh), Makkari (Lauren Ridloff), and Gilgamesh (Don Lee). The Eternals arrive in Mesopotamia in the year 5000 BC. Deviants attack the humans on the land before the Eternals start to fight. Thena wields her spear, Kingo fires energy blasts from his hands, Makkari uses her super-speed to attack, and Sprite casts illusions. Druig also manipulates the minds of the inhabitants to try and fight. After fending off the Deviants, the Eternals introduce themselves to the humans.
Jump to London in the present day where Sersi now lives. She goes to class where she is supposed to be giving a lesson, and she finds her boyfriend Dane Whitman (Kit Harrington) filling in for her until she arrives. The lecture is interrupted by a large earthquake. Sersi has her students go for cover and uses her power to stop a large object falling off the wall from hurting a student.
Sersi later celebrates Dane’s birthday with Sprite and a few others. She gives Dane a ring from his family’s history that she has kept for centuries. While walking on the streets, the three are found by a humongous Deviant named Kro (Bill Skarsgard). Sprite casts an illusion to hide them from it, but the Deviant is able to spot them and goes after them, even though Deviants generally attack humans and not Eternals. Sersi and Sprite ready themselves for a fight before Ikaris flies in and fires his laser eyes at the beast. Sersi uses her power to turn a runaway bus into rose petals. The Eternals see that Kro is also able to heal itself before it escapes.
Sersi comes clean to Dane about her life as an Eternal and what their purpose has been. He asks her why they never helped during the great wars or when Thanos attacked, and she explains that they were instructed to never interfere in the orders of mankind so as to not hinder their development as a society. Sersi also tells Dane that she and Ikaris were technically together for centuries, but things didn’t work out. She later goes back to her apartment to reconvene with Sprite and Ikaris, resolving that they need to get Ajak and the other Eternals together to fight Kro.
Flashback to 575 BC in Babylon – After an intense battle with some Deviants, Ajak forms a link to speak with Arishem. She expresses respect for his grand plan, but appears to have a slight objection as it pertains to the people of Earth. Arishem tells her not to get attached to them and to follow through with the plan. Ajak goes back to the lair where Phastos is developing a steam engine to provide for mankind. The Eternals live among society openly, with Sprite using her powers to entertain children with stories that come to life through her illusions. Meanwhile, Ikaris’s feelings for Sersi have been growing over time. He admits his love to her, which she reciprocates. They make love outside at night and are seen married later during the age of the Gupta Empire with all of the other Eternals there for them.
Back in the present, Sersi, Sprite, and Ikaris travel to South Dakota to Ajak’s ranch, only to find her dead outside her home, killed by Kro. The three mourn their fallen leader, but when Sersi approaches her body, the stone in Ajak’s body that was bestowed to her by the Celestials attaches itself to Sersi, meaning Ajak has chosen her as her successor. Sersi briefly catches a glimpse of Arishem before she loses sight of him.
Flashback: 1521 AD, Tenochtitlan – In the midst of a fierce battle, Thena finds herself overcome by Mahd Wy’Ry, a result of her past memories collapsing in on themselves and driving her insane. She attacks her comrades and nearly kills them before they subdue her. Thena awakens with little memory of the incident. Although Ajak proposes that they go to the Domo and uses the available resources to help Thena, Makkari argues that she wouldn’t really even be Thena after the procedure due to it potentially erasing aspects of her as they already love her. Druig questions Ajak’s leadership as he has long been angry that he cannot use his power to help mankind stop their battles, but knows he cannot intervene. Ajak decides that, since the Deviants have been driven out and staying together would be dangerous, they should all split up and live in the world among the mortals. Gilgamesh agrees to look after Thena and make sure she doesn’t hurt herself or anybody else.
Present, Mumbai – Sersi, Sprite, and Ikaris travel to find Kingo, now a famed Bollywood superstar who has pretended to be his own descendant for the last few decades to maintain an acting legacy. His valet Karun (Harish Patel) knows his secret and has been working with him for over 50 years. The three break the news of Ajak’s death to him, and the threat of the Deviants. Karun encourages Kingo to join his friends on their mission to round up the others, and Karun is even more than willing to join them. They travel in his private jet to Australia, where Sprite expresses annoyance at Kingo for abandoning her a while back for his new famous lifestyle.
In Australia, the team locates Thena and Gilgamesh in their private location. Thena almost has another lapse where she tries to attack her family, but Gil is able to talk her down with help from Sprite. He cooks them dinner before they take the time to mourn Ajak. Later, Sersi tells Gilgamesh about her new burden as leader, and how she cannot figure out how to link herself to speak with Arishem. After relaxing herself, she is able to speak to the great Celestial leader. He tells her that the Emergence is happening, and he explains the true purpose of the Eternals – they were sent to bring forth the birth of the Celestial Tiamut, as new Celestials come about every few millenia and they have done this process on other planets before Earth. They come about through intelligent life, which had been halted by the attack of the Deviants, but with the Eternals having gotten rid of them, Arishem says it is now time to wipe out all life on Earth to make way for Tiamut. Sersi is horrified by the revelation but Arishem defends it by saying this is just the cycle of creation for their life forms. He then explains that Olympia never existed, and that she and the other Eternals are just creations from the World Forge as artificial beings made for use by the Celestials. Sersi cannot remember this because the Eternals have their memories reset after each Emergence. To top it all off, Arishem created the Deviants to regulate the balance between predators and prey so intelligent life may prosper, but he lost control of the Deviants and they became predators themselves. He made it so that Eternals could not evolve to correct his mistake.
Sersi breaks the revelation to the others. They are stunned by the knowledge of their true purpose, but most of them resolve to find a way to save the people of Earth. They figure they must find Druig and see if he may use his power to overtake the mind of Tiamut.
The Eternals (and Karun) travel to the Amazon where Druig is staying in a village where he has been keeping watch over the people for decades. He is not so keen to help the others in their mission, as he has grown cynical and weary over the knowledge of what they were meant to do. At night, Kingo talks to Sprite and states that he knows that she is in love with Ikaris but has not been able to act on it due to her child-like appearance. Soon, Kro and other Deviants attack the village. The Eternals fight them, but Kro overpowers Gilgamesh and absorbs his energy, gaining the ability to walk on two legs and speak English. After he leaves, Thena stays by Gilgamesh’s side as he dies. The other Eternals mourn him. Druig agrees to join the team in honor of Gil, and knows they need to find Phastos now.
Flashback, 1945, Hiroshima – Just after the dropping of the atomic bomb, Phastos stands among the aftermath of the bombing. He weeps to Ajak, feeling remorse for helping humans develop and advance in technology only to continue killing each other. It is here where he loses faith in humanity.
Present, Chicago – Phastos lives with his husband Ben (Haaz Sleiman) and their son Jack (Esai Daniel Cross), and the Eternals find him at their home. Jack recognizes Ikaris from TV from his fight with Kro that was featured on the news. Phastos is not willing to abandon his family for the sake of a dangerous mission, but Ben tells him to go through with it if it means that there will be a future for them and Jack together.
The Eternals travel to Iraq, where they uncover the Domo, as well as Makkari having lived among the locals. Phastos comes up with the idea of linking everyone’s powers together through the Uni-Mind, which will allow them to transfer their powers so that Druig may mind-control Tiamut. When Kingo tells Ikaris that he would follow him to the end, Ikaris tells him that he is not who Kingo thinks he is.
Six days earlier, we see Ajak having gone to visit Ikaris to tell him about the Emergence, and how the Avengers having brought everyone back to Earth after Thanos erased them brought about the energy needed for the Deviants to come back. She has since begun to doubt their purpose and thinks they shouldn’t go through with the mission because of how close they have become with the people of Earth. Ikaris brings Ajak to a location near an icy lake where he has located Deviants. Because he refuses to abandon the mission, he throws Ajak to the Deviants, where Kro goes on to absorb her energy and gain her power. Ikaris flies her body to her house where he will later find her with Sersi and Sprite.
Phastos sends Makkari to locate the source of the Emergence, which turns out to be an active volcano in the Indian Ocean. Ikaris goes to stop their plan, as he soon reveals that Ajak told him about the Emergence after they left Babylon. They realize that he killed her and is planning to go through with the Emergence at whatever the cost. Sprite joins him due to her love for him. Kingo ends up leaving the team with Karun for fear that he will end up getting him killed if they have to go against Arishem. Although Sersi expresses her doubts, Thena assures her that she was chosen by Ajak to succeed her for a reason. Phastos then offers to reprogram the stone in Sersi from linking to Arishem to linking to all of them to form the Uni-Mind.
The Eternals gather by the volcano and begin to battle Ikaris. He seemingly kills Druig and fights the others just before Kro arrives to attack. Thena fights Kro, where he taunts her and nearly absorbs her life force until she slices him to pieces. Sprite attempts to take down Sersi, but Druig emerges and knocks Sprite out. After they subdue Ikaris, the Uni-Mind is activated and Sersi takes on the combined powers of the other Eternals as Tiamut begins to emerge from the volcano. With her powers, Sersi freezes Tiamut and causes it to remain as some kind of statue. Ikaris frees himself, but he feels great remorse for his actions and chooses to fly himself directly into the sun. In the aftermath, Sersi understands Sprite’s frustration with her life, so she uses the Uni-Mind to take away Sprite’s immortality so that she may live a normal human life.
The Eternals split up once again, with Thena joining Makkari and Druig on the Domo as they go look for other Eternals, while Phastos returns to his family, Sprite lives as a human, and Kingo returns to his work, but they all maintain a firm love for one another. Sersi rejoins Dane, who tells her that his family history is more complicated than he realized. Suddenly, Arishem appears in the sky and summons Sersi, Kingo, and Phastos. He tells them that he knows that they failed his plan for the Emergence, but chooses to spare them for now, and then disappears.
Mid-Credits: Thena, Makkari, and Druig are struggling to find other Eternals, as well as their own friends who have vanished. They are then found by a troll named Pip (Patton Oswalt) and his employer, Eros/Starfox (Harry Styles), brother of Thanos and fellow Eternal, who promises to help the other three in their mission.
Post-Credits: Dane is in his family home staring at the Ebony Blade, seeming hesitant to grab hold of it. Before he can make up his mind, an offscreen voice (Mahershala Ali as BLADE) asks Dane if he really feels he is ready.
