Synopsis
The Eternals' Great Machine is failing, which is bad news for the Earth because it is an integral part of the world. And in particular the Resurrection Machine is broken which is bad news for the Eternals. The Prime Eternal Zuras and many others are dead and can't be brought back. It was Thanos who killed them and a group of Eternals have been trying to work out which Eternal has been helping him. They've finally realised it's Phastos who maintains the Machines. They went to confront him but he sicced Thanos on them.
Now we'll find out what it's all about. We begin 1 month ago with Thanos awakening from his latest death which involved falling into a black hole (Guardians Of The Galaxy (2019) #6) with a gaping hole in his chest (after Gamora stabbed him through the heart in Infinity Wars Prime). Phastos is standing over him explaining what's happening.
The Eternals also recently returned from death (after Avengers (2018) #4) and Phastos was the 1st to be resurrected. While he was alone he discovered something which made him consider suicide by throwing himself into the temporal eddies in Titanos. And in 1 of the eddies he happened to see the ruined Thanos. He rescued him and patched him up, discovering in the process that Thanos is a true Eternal, unlike the other Titanian offspring of A'Lars and Sui-San, and so can use the Great Machine. So he gave the Titan access to some of the Machine's systems but *not* the Resurrection Machine. And he now tells Thanos that his damaged body will still kill him. But if he does some work for him then when it's over he will allow the Resurrection Machine to give him a new body.
Thanos knows that Phastos won't really let him live but he expects to be able to get the upper hand at some point and regain his life. But he also knows that Phastos knows he will think like this and expects to outwit him. So the game begins.
We now return to the present where Thanos attacks Gilgamesh, Ikaris, Kingo Sunen, Sersi and Thena to stop them getting to Phastos. They're all in a loop in the Machine's system. The Titan fends off the others while concentrating on Ikaris. But the Forgotten One uses his special bond with the Great Machine to open a portal to a raging nuclear core (or something like that) and throws the Titan in. Sersi then uses a technique she dreamed up after She-Hulk told her how Thanos killed her by suffocating her with a fungus. (That's not how he killed her in Free Comic Book Day: Civil War II, and I can't remember any other instance.) The expert matter manipulator creates 'fungal plasma' which invades Thanos' body and turns his cells into nuclear reactors. Kingo's swords and Thena's spear administer what looks like the coup-de-grace.
In the Reality Loom Phastos is still trying to fix the Great Machine, or at least stop it from getting worse. But he's failing and fears the end of the world.
In New York Sprite is still looking after Toby Robson. Ikaris had a temporal vision in Titanos of regretting not being able to save the boy from death. He's been watching over Toby but left him in the care of Sprite while he dealt with Thanos. Lightning bolts start striking near them in the park as the world gets further out of kilter.
Back in the Exclusion at the South Pole Thanos is refusing to die and everybody's throwing everything at him. But Phastos wants Gilgamesh and Ikaris to help him hold the Machine together. He tells the Machine to eject them from the loop, but it doesn't work like he wanted because they get scattered over the Earth, including Ikaris at the North Pole, and the Machine's teleportation system is now down. So Ikaris just flies from Pole to Pole in a few instants. Phastos tells him to use his powers to reconstruct the 'central span'. As Ikaris rushes off to do it Druig steps out of the shadows and invades Phastos' mind.
We are now treated to 1 of those diagrams, this time explaining the structure of an Eternals' consciousness. The surface consciousness, subconscious and personal memory are analogous to that of humans. But the Machine holds frequent back-ups of the memory which are used during resurrection, including deliberately going back to older states when deemed necessary. It also provides a shared cultural memory. And the core identity of each Eternal is encoded in the 'fundamental structure of reality'. (An ancient(?) attempt to rewrite that code has been redacted from Eternal memory.) There is also another Classified element of the consciousness.
Ikaris uses Eternal matter control to do his designated task. Sersi would have been able to do it easier, but she wouldn't have been able to survive the raging fire of the Reality Loom long enough. The task kills him but not before he succeeds in mending the Machine.
Presumably that includes the teleportation system because Gilgamesh, Kingo Sunen, Sersi and Thena are now with Phastos wanting to know why he sabotaged the Machine and brought Thanos here. Phastos says he can kill Thanos with a thought, but then discovers he's forgotten how. (The work of Druig I believe.) The Great Machine tells them the Resurrection Machine is back online. Then Thena tells it to bring Ikaris back 1st.
We see a representation of a still-glitching Great Machine saying that the effects on the world's ecosystem have stopped and everything will soon be fine.
Later Phastos wants to explain why he did what he did but Sersi recommends they just throw him in the Exclusion until the Uni-Mind can convene and decide what to do with him. Phastos protests that they'll reset his mind to before all this happened, but they have to understand the 'cost'. Sersi pushes for immediate Exclusion but Thena wants to hear him out. He says that while he was the only Eternal resurrected he studied the Machine deeper than he ever had before, and discovered the cost of their resurrections.
We see Ikaris' body being recreated, and then the Great Machine adds the spark of life. And we see Toby Robson die in his bed.
Phastos has now told his 4 listeners what he discovered (ie that every Eternal resurrection requires a human death). And back in Av(2018)#4 they realised that their function of protecting the Earth was now pointless because the superhumans can do it themselves (which is why they committed mass suicide then). So he decided to stop the Machine to stop the killing. But then he found that stopping the Machine would kill the Earth.
Gilgamesh walks away in despair because of all the errant Eternals he has executed. Ikaris joins them and learns the truth, and Sprite turns up to tell them that Toby has just died. Thena remembers how eager Sersi was to shut Phastos away, and realises that she knew all this already. Sersi admits it and says this has happened many times before but only she here retains the memory.
Now Zuras is reborn and calls everyone to Olympia. Ikaris explains what's happened. Zuras agrees to convene the Uni-Mind to discuss it. A bit later Thena asks Sersi what will happen, and Sersi tells them the truth. There are too many Eternals who don't care enough about individual humans rather than humanity. Humans die all the time so what does a few more matter? The vote will go against them and it will be wiped from the protesters' memory. She thinks Thena is right to associate with the short-lived ever-changing Deviants. But what other option is there for the Eternals?
Later we see Ikaris, Kingo Sunen, Phastos, Sersi, Sprite and Thena at the gates of the Deviant city Lemuria. They ask to be let in. They wish to be mortal.