Synopsis
Thanos is staring into Death's Infinity Well for inspiration again (see Silver Surfer #38), and her minion Ratter comes demanding to know why he hasn't fulfilled her command to kill half the population of the Universe yet (see SS#35). He replies that he was seeking a means to expedite the process, and they are transported to Death's throneroom where her spokescorpse asks how this knowledge will help. Thanos says that killing that many beings might take centuries, giving time for forces to arise to stop him, even with the enhanced power his mistress gave him when she sent him back to the living world (SS#34).
But the Well has given him the idea of collecting the 6 Soul Gems (again). Last time (Avengers Annual #7) he was going to use them to extinguish all the stars in the Galaxy. (He failed, and it led to his death in Marvel Two-In-One Annual #2.) But the Well has shown him that the Gems are much more useful than just as a source of raw power, and their current owners don't realise their potential. He asks Death's permission to seek the Gems, and sweetens the pot by telling her that the 1st Gem he'll take currently belongs to the In-Betweener (who angered Death by making her act against her will in SS#17). Death gives her assent. Thanos sits on his Space Throne and leaves.
The In-Betweener works for Lord Chaos and Master Order but he stepped out of bounds when he worked with the Elders Of The Universe to try to kill Galactus in SS#17-19. At the end he was handed over to his masters for punishment. Thanos deduces that he must be imprisoned at the Nexus Of Realities. To get there he has to pass through multiple realities (some of them Ditkoesque) some of which would have killed the being he was before he passed through Death's realm. We see him warped, turned to crystal, melted and shattered, but each time he returns to himself. The journey ends when he shatters a barrier into shards of himself and sees the fulcrum of existence between points of 2 giant tetrahedra, the place where all dichotomies meet including Chaos and Order. There the In-Betweener floats in a force bubble above a small discworld housing 'creatures of mixed reality' as guards (but they just look like winged demons to me). But whatever they are the Titan just blows them all away with a blast from a device at the top of his Throne.
In-Betweener, still trapped in the force-globe, recognises Thanos but thought he was dead. The Titan says he got better, and has come to free the prisoner. IB suggests his benefactor must have an ulterior motive and Thanos claims to want to escape from his thralldom to Death, for which he would need an even more powerful protector. In-Betweener agrees to the deal, but his thoughts tell us that he intends to kill his liberator once free. Thanos suggests that neither of them could break the bubble alone, but their combined powers might do the job. IB exerts all his cosmic might and Thanos blasts away at the outside. After several panels of straining the bubble cracks and the prisoner is free.
In-Betweener then justifies his next move by saying that Thanos has proved his untrustworthiness by betraying Death. And he points a finger at the Titan. But nothing happens except his saviour hits him, saying he would never betray Mistress Death. And then he takes the Soul Gem from the brow of IB, who is confused why his powers don't work now. Thanos explains that the In-Betweener draws his power from the conflict of polar opposites like Chaos and Order, but here at the Nexus all such dichotomies merge. However his kind jailers had arranged for his powers to work *within* his prison bubble, but if he ever escaped that he'd be helpless.
Thanos also adds that Chaos and Order couldn't detect *his* presence here because he is outside such dichotomies. (Later I believe he will attribute this to his return from death, which would mean that very many of Marvel's super-chars must be in that state by now.) But by now they will have detected IB's escape and will soon be here to put him in a worse prison. Thanos and his Throne leave. Lord Chaos and Master Order arrive and IB tries to blame everything on Thanos. I don't think they believe him.
Back in normal space Thanos contemplates the green gem that once belonged to Adam Warlock. He muses that this is the only 1 of the 6 Soul Gems that deserves that name because it can manipulate souls. But his thought are interrupted by Death and her spokescorpse who asks if Thanos meant it when he said he wanted to be free of their mistress. The Titan protests that it was a ploy to trick the In-Betweener. It seems Death believes him and they leave. Thanos has now had it confirmed as he expected that Death is watching his every move, so he must be extra careful that she doesn't uncover his true plan before he is ready.
His next stop is the planet Tamarata which is continually fought over by 5 Galactic federations. The Elder Of The Universe Champion loves it here because he can always find an army to fight. He wears a Soul Gem but doesn't realise it is the source of much of his power (despite the fact that he used to just fight individuals but since getting the Gem he's upped his game to armies). Thanos arrives on his Throne and sets the teleport to 'remote external function'. He then challenges Champion to a fight. 1st he dodges the Elder's blows while landing his own. Then when Champion decides on more cautious tactics the Titan switches to continuous blasts. His foe gradually forces his way ahead through the barrage, but when he gets very close Thanos stops firing and the Elder pitches forward to meet a power-enhanced fist. For the next stage Thanos erects a forcefield for Champion to batter himself against. Then the Elder chooses the move the Titan was waiting for. He power leaps up into the air and then plummets down towards his foe ...
... who activates the Throne's remote teleport to take him out of the way. Champion hits the ground with 'the power of an atomic arsenal'. The resultant shockwave ignites a dormant chain of volcanoes, followed by a chain reaction which blows the planet to pieces. Champion survives but is stranded in space amidst the rubble. Thanos also survived too thanks to his Throne, but he doesn't feel like fighting anymore so prepares to leave. The Elder begs him to take him to another planet. Thanos agrees if he'll give him the Gem on his brow. Champion gives up the useless bauble, and the Titan *does* deliver him to another inhabited planet. But he leaves him miles above the surface with a long fall ahead.
Thanos contemplates the red Power Gem he has added to the collection he is accumulating, which he now renames the Infinity Gems. And he's ready for the next opponent.
Thanos meets the Gardener and we learn that he originally sought out a Soul Gem to help him create beautiful gardens, but he lost it. But this led him into the scheming of the Elders (in Steve Englehart's issues of Silver Surfer) in order to regain it. Now he's turned his back on such things and returned to his gardening. After touring his latest production they sit on benches facing each other and calmly discuss their conflicting goals. Thanos must have the Gem and Gardener won't give it up without a fight, even though he knows it's 2 Gems to 1.
We see Thanos gradually enclosed in thorny brambles. But then he bursts free of them and tells Gardener that (like the other 2) he doesn't realise what he has. Thanos has discovered that the Gems 'come from before all recorded time' and he believes they might be the cornerstones of reality. The Soul Gem controls souls. The Power Gem provides infinite power to the other Gems. And now he will have Gardener's orange Time Gem which had been used subconsciously to create the marvellous plants - by taking them rapidly through their growth span and then freezing them in time at the height of their beauty. But now that beauty crumbles. And we see that Gardener has been internally invaded by plants and is seemingly dead. Thanos says he used the Power Gem to increase the effects of the Time Gem on the plants.
And now Thanos takes his leave, musing how fairly he has dealt with his opponents so far.