Synopsis
The Eternals (re-)discovered that they are only immortal because whenever they die they get resurrected at the cost of a mortal's life, human or maybe Deviant. Now our main chars, the Eternals with a conscience, have gone to live with the Deviants to learn how to avoid dying. Meanwhile in their absence Thanos of Titan has succeeded in being elected the new Prime Eternal, after temporarily killing Zuras again. But he knows that the body Phastos made for him has a weakness which the smith has been made to forget. Phastos has gone the the Deviants to try to rediscover that secret. However Thanos also knows that Phastos is also the only 1 who can completely cure him. So he's brought the Oceanic Watch, whose task was always to watch the Deviants and destroy their city Lemuria if they got too dangerous, to fulfil their destiny unless Phastos is handed over to him.
Sersi is mentally summoning the other Eternals to the battle. Ikaris leaves off learning defensive fighting with the Deviants Karkas and Ransak. Sprite calls Thena from the arms of her Deviant lover Tolau. Sersi tells Kingo Sunen to guard Phastos while he continues to find a way to kill Thanos. The Oceanic Watch unleash atomic cannons from above - Thanos doesn't care if Phastos is killed because he'll just get resurrected by the Machine. The Deviants fire Eternal-seeking missiles, but more effective is Ikaris punching through the cannons. Sersi and Sprite are fighting against individual Watch members, but whenever Sprite is hit she turns out to be an illusion.
Thanos takes a hand personally. He drops down to the surface of Lemuria and demands to know where the Eternals are living. He's pointed towards the sculptor Tolau The Delirious who's holding his latest exhibition nearby. The Titan goes there to see 2 figures - Eternal Thena sculpted out of (the weaker secondary) adamantium and Tolau himself built from perishable meat. He pauses to admire and then critique the work. He fires a blast which melts both statues proving that the intended contrast was false.
He doesn't try to force Tolau to betray his lover but merely waits a short while for her to come running. He asks Thena where the smith is, with his hand round the Deviant's throat. Tolau reminds her he's dying of the Excessive Deviancy disease so Thanos killing him would be a mercy. But Thena still directs the Titan truthfully to the cellars beneath the Takarina Express. Of course Thanos prepares to kill Tolau anyway, claiming it will increase the value of his artwork. But on the other hand he doesn't want to get the reputation of being merciful so he leaves the Deviant to his painful fate.
Thena mentally tells the others what she has done, rationalising that it will save many Deviant lives. Tolau points out that it hasn't saved him because the big Change has started that will make him Excessively Deviant. And they both know that the Celestials created an unstoppable drive within every Eternal to destroy Excessive Deviation. He begs her to leave him because he doesn't want her to have to kill him and then have to live with the guilt. The Machine tells us that Thena fantasises that she will overcome the drive to kill Tolau and will nurse the monstrous thing he becomes until she can find a cure for him. But she knows deep down that will never happen. Tolau transforms, Thena's hard-wired nature takes over and she rams a sword through his chest. She rationalises that *someone* would have to kill Tolau and it were better someone who loves him.
After Thena's warning Kingo drags Phastos away from his science lab before a blast from above destroys it and many Deviants in the area. Phastos can't take any more blood on his head so he plans to surrender to the Titan to buy time for Kingo to continue his work. Of course actor Kingo protests that he can *play* a scientist but he isn't 1. So Phastos leaves a big clue for him and the others. Thanos is an Eternal but he is also somehow a Deviant. Eternals can't give birth to Eternals, so whatever Mentor and Sui-San did to produce him (and Eros) must involve a Deviant element. So they need to investigate the Deviants' deepest secrets.
He then steps out into the open and calls down Thanos. The Titan obliges and beats him to death knowing that he will be reborn back in the Exclusion in Olympia. But Thanos still tells the Watch to raze the city. However Druig contacts him from Olympia to point out that such an unnecessary tactic might allow the Eternals to capture 1 of the Watch. And the Watch will prove useful again in the future. So the Titan calls his hounds off and they all leave.
Sersi meets up with Deviant Warlord Kro who is taking his people's disaster philosophically. The Oceanic Watch only did what they were designed to do, and we learn that they've done it before. But then Thena joins them with her personal grief. She and Kro have a long history including being lovers, and he commiserates with her. They know that Eternals are coded to 'prevent excess deviation' by killing such Deviants, but now she expresses her intention to do it by finding a preventative cure. Kro warns her that Deviant scientists have spent lifetimes working on the problem, but Thena points out that's as nothing to an Eternal.
Ikaris, Kingo and Sprite join the conference. Sersi says they need to use the time Phastos has bought them, while Thanos tries to pry his secrets out of him, to discover how to kill the Titan. Kingo passes on the lead that Thanos is part-Deviant and Phastos thinks the weakness he built in to Thanos' current body is connected to that. So they need to learn more about Deviants, such as *why* the Celestials created them in the 1st place. Kro says their priesthood have theories and Celestial lore but they're unlikely to grant access to Eternals, especially after today. So our Eternals go consult their own priests ...
... in Celestia in an Andean valley (which we are now told is a constructed conceptual valley sculpted from a condensed belief matrix). Ajak and Makkari greet them. Ajak reiterates that Eternals can't beget Eternals, and to succeed would require a change, ie a Deviancy, which would be heresy. Makkari is more practical. They can no longer gain Celestial knowledge because their Celestial gods won't talk to them anymore. However they both know that there is a last Celestial on Earth, but Ajak says it is guarded by their greatest foes. Not the Deviants but the blasphemous humans who inhabit the Celestial corpse - the Avengers.