Pretty much all the Marvel characters – Avengers of every flavour, the Thunderbolts, most of the Fantastic Four, the Hood's syndicate of supervillains, and a bunch of lone wolves—are in pitched battle with the Skrull invasion forces, led by Skrull Queen Veranke, who is disguised as Spider-Woman.
Yeah, that's really all the background you need.
Leinel Yu delivers a massive battle sequence, filled with detail: it's the sort of work you want to study so you can capture all of the nuance in the background. If you want a point of comparison, in my opinion it compares favourably with the stuff George Perez was producing in JLA/Avengers. Lots of good stuff happens:
Wait. Jarvis' custody? That can't be good...
Anyway, after the Young Avenger Hawkeye is felled by an attack, Old Avenger Hawkeye (a.k.a. Ronin) picks up her (a.k.a. his) bow and shoots a bunch of Skrulls dead, most notably Skrull Queen Veranke. That isn't as good news as it might sound, because it provokes the watching Skrulls into launching their scorched-earth counterattack.
What sort of counterattack? Well, recently "Yellowjacket" tricked the Wasp into giving up her old growth formula for a new one he had devised. Seems there's more than just Pym particles in that formula, because with the press of a button, the Wasp screams. She also begins to grow, and to exude lots of Kirby-style purple energy. This energy engulfs everyone in the battle.
That can't be good either.
This is one breathless issue. Most issue-long battles are a snore to read, but not this one, largely because there are so many participants everyone can provide the best they've got to offer and don't wear out their welcome. So Brian Bendis' writing is part of it, but the smaller part. The larger one is Leinel Yu's art, about which I can't say enough good things. This is art that's not only gorgeous to look at, but rewards close study. Kudos to both men for delivering.
It's not a must-read issue, because it's got no real beginning or end: in no way does it stand on its own. You couldn't start here and you certainly wouldn't want to end here. And so I don't think I can give it five stars. (The cover doesn't help in this regard either – see below.)
But it more than earns its four stars. If only every arc could have a final act that performs this strongly.
It will not surprise you to learn that the scene on the cover appears nowhere in the comic. But hey, I hear the kids will buy anything with Spider-Man or Wolverine's picture on it.