After being cast into the Ultimate universe during a fight with Mysterio, Peter Parker has learned that his Ultimate universe counterpart died in battle and has been replaced by a young teen, Miles Morales. Peter also visited the Aunt May and Gwen Stacy of this world, but now has to find a way back to his own dimension.
At his base in the 616 Marvel world, Mysterio thinks that he's trapped Spider-man in a dimension he can't escape from, and that he's destroyed him because of that fact. He wonders why that isn't enough, and realizes he has to actually see him suffer and die. He fires up one of his avatars, and opens the 'dimensional vortex'. As he does, weblines shoot out of the dimensional tunnel, catching Mysterio and pulling him in. On the other side, he finds Spider-man, Miles, Iron Man, Fury and Thor waiting for him in Mysterio's lair in the Ultimate world.
Fury says the only one going back through the portal is Spider-man himself. Spider-man tries to find the words to say goodbye to the Ultimate universe counterparts, when Mysterio busts loose and gets to a computer keyboard, types something. Explosions rip through the hideout, catching everyone off guard. Mysterio then drops a few vials which break open on the ground--a compound that causes the heroes to see their worst fears: Iron Man sees his fellow Avengers decimated; Fury looks upon a city in firey ruins; Spider-man sees his Aunt May impaled on one of Doc Ock's tentacles. Miles sees his parents shot dead by his Uncle Aaron as The Prowler. Spider-man tells everyone they are just Mysterio's illusions and to push through them.
Miles tackles Mysterio and they go flying back through the portal. On the other side, Miles pauses to look out the window at the alternate city. Mysterio is about to club him, when Miles does a backflip over him, and kicks Mysterio back through the portal. Fury places Mysterio under arrest, and agrees to keep him in that dimension. Iron Man tells Spidey he has to leave now, as the portal is becoming more unstable. He gives Miles his blessing to do the Spider-man thing in that world. He also tells Miles "don't let anyone clone you," among other things, before the portal closes, cutting him off in mid-sentence. Fury tells Miles that he's got Spider-man's blessing, now he has to keep earning it.
Back in the regular Marvel universe, Peter is at his apartment, and wonders if there's a Miles Morales in that world. He enters his name in a search engine. The last panel shows a closeup of Peter's face as he says "oh my god".
And so ends Marvel's first crossover between the regular Marvel continuity and that of the Ultimate Marvel universe. This issue is brief and to the point, and does a decent job of wrapping up the story.
Mysterio doesn't exactly go down easy here, but he was a bit too disposable this issue for my liking. And he's now trapped in the Ultimate dimension, which means no more 616 Mysterio (until his inevitable return). Pichelli's Mysterio looks a little too Lex Luthor-y to me throughout this issue. Otherwise, the art and coloring is top-notch throughout.
I wonder what the ambiguous ending is meant to imply, as Peter searches the name Miles Morales in an internet search engine. Does he find him to be a criminal or murderer in the world of 616? Certainly seems like the door is being left open for another crossover, and perhaps an appearance by Miles in the 616 at some point.
This crossover was relatively light and entertaining. Again, there's very little conflict and the outcome is rarely ever in doubt, but it was cool to see Peter and Miles team up.
Again, it'd be great to see this crossover referenced in the main book, but as there's basically no interconnectivity among titles anymore, it's probably not happening.