Five years after Endgame, portals started appearing all over New York. They would materialize during the night in flashes of bright light and intense noise, deposit something or someone, then disappear. No one knew what was happening or how the portals were appearing until a few weeks ago when the newest and potentially the most dangerous supervillain yet appeared. He dubbed himself 'The Conjurer'. His claim was to even out the world in a different way than Thanos; he would bring people from other dimensions here, and send people from Earth to those dimensions to replace them. Now, using the people and creatures he's summoned, Earth has to form an entirely new team to defeat him if they ever want to get home again.

"Hi. I'm Clint Barton. Five weeks ago, you were all summoned here from your universes by the Ar-"
"Language!"
"Ahem. By the . . . man . . . who calls himself The Conjurer. This world may seem strange, or primitive, or advanced, or backwards, or even impossible to you, but it's ours, and we'll defend it to our last breath. Besides, the only way you can get home is by working together to beat this guy, anyway. So . . . Are you in?"
" . . . "
"Not very talkative, are we? Well, that's fine. We'll leave you to get acquainted with the rest of your soon-to-be-teammates."
" . . . "