Synopsis
This issue centres around The Sentry (and Skrulls).
Years ago in his 1st active period (the 1 we've all forgotten) Sentry once again faces his nemesis The Void, who is actually his own dark side. But at this point Sentry doesn't know that. In fact it seems he believes he'd killed Void some time before, but Void continues to maintain that's impossible (because he knows they are the same person).
Their fight is interrupted by the sight of an alien spaceship trying to ram the top floors of the Baxter Building. Sentry stops it from killing the Fantastic Four, and drags it back into space. Inside he finds green aliens with pointy ears and corrugated chins. Commending themselves to their god they self-destruct their craft.
Bob Reynolds wakes up in the medical care of his pals the FF. They tell him that he's just encountered Skrulls, who hate them for various reasons. The reappearance of the Void has affected Sentry deeply.
Skip forward to a few months ago in Avengers Tower (with Sentry's Watchtower on top). Edwin Jarvis (who's really a Skrull replacement) is serving refreshments to the New Avengers (in NAv#15) before they publicly announce their team. Sentry is there with Captain America, Iron Man, Luke Cage, Spider-Man, Spider-Woman (also secretly a Skrull - Queen Veranke) and Wolverine. Ms Marvel drops in (for a blueberry muffin if nothing else).
Jarvis asks Tony Stark if he can review the files on Sentry. After the recent breakdown of Scarlet Witch (Avengers Disassembled and House of M) he's worried about something similar happening to Bob Reynolds. Tony assures him that Wanda's problems weren't his fault or responsibility. But he gives him full access to all Avengers files - because there's no-one he trusts more. (I would have thought Jarvis had such access anyway.)
Jarvis hungrily devours the information and takes it to a meeting with Veranke plus the Skrull replacements of Elektra, Henry Pym, Val de Fontaine and sundry Hydra and SHIELD Agents. Sentry is the most powerful current Avenger, but they can't replace him because they can't duplicate his powers - because no-one knows exactly what they are. Jarvis thinks it's too dangerous to plant an agent close to him by replacing say his therapist because he may detect him and reveal the Invasion.
But in his opinion they don't have to worry about Sentry. He's insane. He created the Void to do as much evil as he does good. Having his memory wiped and being erased from the world's memory made the situation worse. And then Mastermind tampered with his mind. With his mental problems they just have to wait for him to self-destruct. And if he doesn't do that of his own accord they just have to imitate the Void and suggest that the whole Invasion has been masterminded by his other self.
They also discuss other things that are going their way. The Hulk situation and the Registration Act will tear the superhero community apart. Thor is gone, and so is Scarlet Witch. Jarvis also believes that Dr Strange will fall too.
Now to current events. The New and Mighty Avengers are in the Savage Land where they've met a group of heroes, some of them their duplicates, who claim to have been captives of the Skrulls for years. Both sides maintain that they are human and the others are Skrulls. Inevitably they are fighting (as seen in Secret Invasion #2).
(We will of course discover that the 'captured' heroes are really the Skrulls. But NAv#43 will explain that, unlike replacements such as Jarvis, these have been conditioned to believe that they are the real human heroes. This is a ploy to enhance the distrust and confusion that already has the Avengers at odds with each other.)
We now get a replay form SI#2 of Sentry fighting the Vision (currently destroyed as of Avengers Disassembled). He at least seems to know he's a Skrull because he uses the very ploy of pretending to be the Void and saying that Reynolds engineered the Skrull Invasion as revenge for the heroes forgetting him.
This issue now shows us that Sentry panics and flies to Saturn and goes into a foetal trance.
Later in Times Square (between SI#2 and #3) the Young Avengers, including the new Vision Jonas, are fighting the new breed of Super-Skrulls. In the Watchtower the AI CLOC wakes up Bob Reynolds' wife Lindy. She's attacked by a Super-Skrull but the Void saves her, his dark form now in the shape of Sentry. He says Bob isn't in a position to help her now, but he'll take care of her. Lindy is more terrified of him than of the Skrull.