[The story] begins [in April 2012] with an extinction-level event barreling its way toward Earth, namely the cosmic entity of death and rebirth known as the Phoenix Force. It’s looking for a new host who will possess all of its power, which may or may not be the mutant teenager Hope Summers.
Cyclops, Wolverine, Magneto and the other X-Men want to protect her and prepare her if she’s to be the new Phoenix. Captain America, Iron Man, Spider-Man and their fellow Avengers want her handed over to them so they can figure out what to do with her and keep the world safe from a potentially fiery fate.
Suffice it to say, tensions — and fisticuffs — arise.