Synopsis
The 'previously' page of flashbacks shows Black Swan and Reed Richards' explanation to the Illuminati that 'incursions' are 2 alternate universes touching at the Earth. At that point they will have 8 hours to solve the problem. At the end of that time both universes will mutually destruct. Unless 1 of the 2 Earths is destroyed, saving both universes. Captain America absolutely refused to countenance killing a world. They must find another way, and he proposed using the Infinty Gauntlet. Later Reed and T'Challa agree that if Cap's plan doesn't work, they'll have to consider destroying other Earths.
As part of Charles Xavier's will, Beast receives an envelope containing the word 'remember'. This triggers a hidden memory where Xavier told him about a locked room containing information about his 'clandestine activities' - and something else. Now Beast also remembers the keyword to gain entry to the room. Inside he finds a blue gem (the Mind Gem). And Lockjaw teleports Black Bolt, Captain America and Sub-Mariner there, with the other 5 Infinity Gems, to invite Beast to join the Illuminati (replacing Prof X).
Next day, in the Wakandan Necropolis, Dr Strange and Mr Fantastic implant a device in Beast's palm, even though he isn't sure he agrees to join them. Namor thinks Henry McCoy isn't up to it. But Reed Richards has faith in Xavier's choice.
The device will pass simple messages between the Illuminati. It also acts as a homing beacon. And thirdly it will react to the early warning system that T'Challa and Tony Stark have built, to warn them of an incursion.
Mr Fantastic interviews the prisoner Black Swan again. He tells her that they intend to use the Infinity Gems (combined as the Infinity Gauntlet) to stop the next incursion. She recognises them from his description, and agrees that they will have some effect. (But only in this, their native universe.)
4 days later she detects an incursion, and the Illuminati's palm implants alert them. They track the incursion to the Pakistani Himalayas. But Lockjaw couldn't teleport them inside the incursion wall (just as Black Panther couldn't port out in #1). Iron Man detects the boundary, but they only have 6½ hours left.
The Illuminati walk through the invisible wall, and find themselves in the red atmosphere Panther had described, with another Earth hanging in the sky getting slowly closer. And the 6 members with Infinity Gems (not Black Bolt and Black Panther) join them together to form the Gauntlet. This is immediately sensed by the Watcher on the Moon, Thanos on Titan, and even Galactus far away in space.
Reed and Tony elect Steve Rogers to use the Gauntlet. They say that his willpower, and his belief (in his own idea), will be important. Namor pooh-poohs this, but Beast concurs. Cap dons the glove and aims its power at the other Earth. He's got to not only push that Earth away, but the whole universe that contains it!
Cap slows the other Earth's approach, and then starts to push it back. But Iron Man detects feedback.
With a mighty flash the other Earth vanishes. But so does the Time Gem. And the other Gems shatter.
Sub-Mariner blames Cap for losing their only effective tool. The other Illuminati have to pull him off Cap. While Beast looks on in disgust.
Later, back at the Necropolis, Cap is taking a break from a long argumentative meeting. Panther comes to bring him back to the table. Steve is still dead set against compromising his principles. He asks T'Challa for his support. T'Challa promises to do the right thing.
But Black Panther reveals himself to be on the other side in the resumed meeting. He has a duty to protect his people. So do Black Bolt and Sub-Mariner, and Beast to save mutantkind. And Mr Fantastic his family. Steve appeals last to his brother-in-arms Iron Man. But Tony just apologises for what they're going to do next.
Dr Strange casts a spell. And Cap falls asleep, with his memory of these 3 issues wiped.