Six Avengers plucked from various times (Captain America, Captain Marvel (Genis-Vell), Giant-Man, Hawkeye, Songbird and Wasp) escaped from Immortus's castle in Limbo, leaving a 7th Avenger Yellowjacket behind, and all they have to show for it is a synchro-stick. Returning to the time-Sphinx they got from Kang to keep Rick Jones hidden from Immortus, they found Rick had left in a chronosphere. And they don't know that Yellowjacket has made a deal with Immortus.
Immortus previously used synchro-sticks to show Avengers parts of history. Hawkeye tries to make the stick talk to him. But when he gets rough with it, it reveals itself to be a Space Phantom. As were the previous versions. Space Phantom's power to replace people won't work outside time in the Sphinx, so he's trapped. It turns out this was the first Space Phantom that Avengers met, in Avengers #2. For some reason he is Immortus's favourite. They persuade him to tell them all about Space Phantoms and Immortus, which takes up the majority of this issue.
I have included lots of background information directly into this description, for 2 reasons. They are more integral to the story than in earlier issues. And if I had relegated them to the Notes section, the Notes would have been bigger than the main description.
Phantom explains that beings who get trapped in Limbo slowly forget their previous existence and turn into Space Phantoms. They can't escape from Limbo, except when Immortus sends them on missions, mind-controlled to believe whatever cover story he has told them. Captain Marvel uses his cosmic awareness to check that this Phantom isn't mind-controlled in this way.
The planet Phantus, home of this Space Phantom, was an illusion generated by Immortus in Thor #281-282. It was part of a scheme to get Thor to deplete the time-travelling power of his hammer Mjolnir, thus depriving the Avengers of a handy method of time-travel. This was part of Immortus's overall plan to keep Avengers under control.
Soon after Kang became Immortus and settled in Limbo to study the multiverse, he was recruited by the 3 Time-Keepers to safeguard 7 millenia of the timestream. One of the things they wanted him to do was destroy the Avengers, at least as a group. In Avengers #2 he sent this Space Phantom to turn the Avengers against each other, mind-controlled to believe he was the advance scout for an alien invasion. Then in Avengers #10 he allied with the Masters of Evil, sending Phantoms disguised as Merlin, Hercules and the biblical Goliath against the Avengers. When the plan failed, Enchantress reversed time back to before the Masters of Evil met Immortus, and sent the main Marvel universe down an alternative timeline when they turned his alliance down. Which is why Avengers don't remember this adventure.
At this point Immortus took a shine to Avengers and persuaded Time-Keepers to let them remain together as long as he kept them in check. However the Time-Keepers didn't like the way Avengers intervened in the Kree-Skrull War in Avengers #89-97, especially the way Rick Jones manifested the Destiny Force (what the Kree Supreme Intelligence called the Human Evolutionary Potential in #1). They showed him how this would allow humans to spread through the galaxies, either as conquerors or by outcompeting other races, sometimes resulting in galactic destruction. Immortus strook a new bargain with them, to keep humans confined to Earth. The alternative is to destroy humanity completely.
This was what he was doing in 2 alternate realities visited by the 7 Avengers in #4-6:- manipulating the survivors of the future War of the Worlds so they wouldn't pursue the 'Martians' into space; deleting a timeline where the exposure of a Skrull impersonating Richard Nixon would lead to xenophobic assault on alien races. But he couldn't achieve this 2nd effect before gaining the Forever Crystal in #3, nor the 1st effect without leaving undesirable alternate timelines.
As well as Rick Jones, the Time-Keepers were also worried about possible powerful children of Scarlet Witch. Immortus conceived of a scheme to prevent such children by arranging a barren marriage for her with Vision. Vision was already attracted to the Witch. Immortus led up to it with a plan to bolster Vision's self-confidence to do something about it.
He sent Space Phantom to work with Grim Reaper in Avengers #106-108 to tempt Vision with Captain America's body. We are now told this was designed to make Vision realise he didn't need a human body to be human. Then in the saga that ran from Avengers #131 to Giant-Size Avengers #4 Immortus gave Vision a past by showing him he was the Human Torch, and officiated at the marriage of Vision and Scarlet Witch.
But the Witch frustrated Immortus's plan by magically giving birth to twins in Vision & Scarlet Witch v2 #12. Unknown to her they were actually fragments of Mephisto's soul, which Mephisto sent Master Pandemonium to reclaim. However the Witch's bond with her children was too strong, so Immortus decided to weaken it by destroying her link to Vision. He arranged for the US government to dismantle Vision and rebuild him as an emotionless machine in the issues leading up to West Coast Avengers #45. He sent a Space Phantom to impersonate (the dead) Prof Horton and deny any connection between Vision and Human Torch in West Coast Avengers #44 and Avengers West Coast #48.
As part of this scheme he went back to before the creation of Vision and used the Forever Crystal to split Torch's body into 2 alternates, but keep them both in the same timeline. Thus Ultron could use one body to create Vision, leaving another body to get buried in Sub-Mariner #14. The revival of this Torch in Avengers West Coast #50 was the last straw for Scarlet Witch, allowing Mephisto to absorb her 'children' in AWC#52.
The Space Phantom next comments on the Kree/Shi'ar war known to us as the Operation: Galactic Storm crossover beginning in Captain America #398. Once again Avengers were interfering in galactic affairs, and Immortus took subtle control of Iron Man via the mental link to his suit. His intervention allowed the Kree Supreme Intelligence's plan to decimate his own race to succeed, as it would have done without the Avengers. However the same intervention caused Iron Man to lead some other Avengers in killing the Supremor in Avengers #347.
The Time-Keepers were unhappy again. They foresaw that Avengers would now be joined by the Shi'ar Deathcry (which actually happened in Avengers #363). They predicted that her description of the Shi'ar's cruel rule over the Kree would spur Avengers to attack Shi'ar, leading eventually to the Interstellar Avengers Corps and the Terran Empire seen in #1. They wanted to destroy Earth, but Immortus persuaded them to give him one last chance.
Immortus foresaw the coming of Onslaught (and presumably the disappearance of Avengers into the Heroes Reborn universe). He figured he only had to keep them occupied until then. So he devised what we call the Crossing/Timeslide crossover ending in Avengers #395. He himself impersonated Kang, with Space Phantoms taking other roles such as Moonraker/Libra (which is why Libra denied any knowledge of it in #2). Immortus increased his influence over Iron Man, causing him to commit murders. As Kang he suggested that he had also been responsible for Hank Pym's breakdowns, but Space Phantom says this was a lie.
This brings us to the current situation. Immortus tried to kill Rick Jones when he regained the Destiny Force in #1, to stop Time-Keepers from just destroying humanity. Time-Keepers want to keep the universe safe from mankind.
At this point Immortus and Yellowjacket secretly arrive. Yellowjacket has used Limbo's insects to find fellow insects that Avengers inadvertently brought with them to the Sphinx. Immortus zaps the other Avengers without them realising who has done it.