Synopsis
Loki is in the Library in Omnipotence City which houses the Parliament Of Pantheons (as seen in several issues of 2012's Thor: God Of Thunder series). He's worried that some of the books describe events differently from how he remembers them. There are also many variants of the same stories. There are only 2 constants - he's never the hero and he never wins the throne. (I'd say he has gained the throne of Asgard a few times but he always loses it eventually.) He thinks it's a conspiracy.
His musing is interrupted by Flowa, an Asgardian Tomekeeper who wants to throw him out because the Library is closing. He protests that the books are contradictory. They often ignore what was written earlier to tell a tale differently. And what's with all these copies of people in different universes? (I need hardly say all this is actually a critique of the fictional Marvel Universe.)
Flowa takes him to see a book he might find interesting. Along the way she mentions that Freya took the precaution of keeping copies of the most important Asgardian books here. Which it turns out was wise considering that Asgard was recently destroyed by falling into the Sun. (Actually Asgardia in Thor #705. The old ruined Asgard still exists. #706 shows the Asgardians rebuilding it, but the latest Avengers series shows Odin alone in it.)
Flowa shows him a book she hasn't read about a war within a family and a war between worlds. But when Loki opens it they discover that most of the pages have been ripped out. Flowa is incensed. All she can remember (being told) about it is that involves a quarry at the end of space. Loki asks if it is the God Quarry (seen in Thanos (2017) #8-12). Flowa says that the lowest level is known as the Quarry Of Creation.
Loki decides to visit the Quarry and asks Flowa to accompany him for her useful knowledge. She agrees because she always wanted an adventure, and she might get to *write* a book about it.
Adam Warlock is visiting Doctor Strange. He describes what he saw when he was last in Soul World (inside the Soul Gem) - a desolate dustbowl (in Guardians Of The Galaxy #150). (We didn't see then the image we are shown here of inhabitants continuing with their lives but in sepia tones rather than the brightly-coloured Utopia of yore. The bald figure playing the saxophone suggests that Drax has a soul fragment trapped in that world, not just Gamora.)
Strange protests that the Infinity Stones no longer exist. Warlock counters that he believes they *can't* be destroyed, and asks if he has the Time Stone. Stephen Strange ignores the question and instead asks if Adam is trying to assemble the complete set, which would be a *bad* idea. Adam admits to having the Soul Gem, taken from Ultron (Infinity Countdown #4) with help (Galactus and Silver Surfer). DrS is more concerned that Warlock has been associating with Kang (he can sense the tachyons).
Instead Stephen produces the Ropes of the Xiand Nomads (something he picked up between the scenes in his space travels in the as-yet-incomplete DrS(2018)#1-5) which can cross dimensional barriers. He tethers them together and sends Adam into Soul World to scout out the situation. Inside Warlock finds a sandstorm and people fleeing from an approaching indistinct giant monster.
Adam says he's powerless and warns Stephen not to follow him in. This just prompts the Doctor to send his astral body to investigate. He finds Warlock impaled on a spiky leg of the monster. Strange's astral form retreats back home to join his body ...
... which pulls the Time Stone out of his pocket. DrS uses it to nip back in time a few seconds and warn himself to pull Warlock out of the Soul World straightaway. He also pops inside to tell Warlock to get out before the monster gets him.
When they're all back together in the present in Strange's Sanctum Sanctorum Warlock complains that Doctor Strange didn't tell him he had the Time Stone (he stole it from Super-Skrull in DrS#3). Strange counters that Warlock didn't tell him that Kang smuggled him into the present (in IC: Adam Warlock). Stephen pours them a drink and relates how Gamora showed him the desolate state of Soul World (in All-New Guardians Of The Galaxy #12), but it's much worse now. Adam says that's why he wouldn't open Soul World for Gamora to retrieve the fragment of her soul trapped there (IC#5).
Stephen suggests Adam leave the Soul Gem in his keeping. Warlock now suspects that *Strange* is trying to collect the set. DrS asks him what he promised Kang in return for his help. Adam admits it is the Time Stone. Strange throws him out but Warlock warns him that others will be looking for the Stones too, especially Thanos ...
... who we see on his throne on Chitauri Prime with the Chitauri warriors who will obey his every whim. He currently feels invulnerable because he has been to the future and seen his immortal future self (Thanos (2017) #13-18)
He knows the Infinity Stones are active and is determined to make them his own once again. He will send out the Chitauri army to cause distracting chaos while he himself slips in and takes the Stones from the lifeless hands of their current wielders.
But he doesn't see the figure behind him, hooded, armoured and with a *big* energy-sparkling sword. (This is the person we've seen having the armour and sword fashioned by an Asgardian Dwarf in the opening pages of each issue of Infinity Countdown.) Thanos is stabbed through the chest and turns to see who did this. He recognises the person and the design of the sword and guesses it's time for his requiem. The wielder responds by chopping his head off. As Thanos dies he is glad that the future self he saw won't come to pass.
The Chitauri say that they now serve the killer of Thanos. But the figure, now sporting a gas mask, lets loose a gas which kills them all. The person stamps on the Gauntlet that once housed the Infinity Gems, and reflects that now her (spoiler) past is dead and her future can be written.