It’s the New Mutants versus the Avengers!
Or, more exactly, The Avengers vs. Magneto and Warlock.
The resurrected (by Beyonder) New Mutants are taken by the White Queen and recruited as Hellions, so Magneto and Warlock go on a rescue mission. Magneto let them go to her Academy because he didn’t want to “force” them to say at Professor X’s school, given that they had reservations about the former leader of the Brotherhood of Evil Mutants leading the School for Gifted Youngsters.
The Avengers find out that Magneto is leading a strike against a “school,” and race off to intervene.
When Magneto starts to lose, the other New Mutants (now Hellions) show up—teleporting using Magik’s powers—and pull Magneto out of the battle, seeing him as the “good guy” in the scenario. His actions—racing to save them from White Queen, and standing up to the entire Avengers just to fight on behalf of these kids—convince them that he does in fact have their best interests at heart and is a worthy successor to Professor Xavier.
So some development of the overall story, but mostly this is just a fun, big fighting story.