Kitty is researching Norse mythology after the X-Men's recent Asgardian experience. She's supposed to be meeting up for food with Illyana later, but instead ends up with Magik's armour and soulsword, and is attacked by a demon. Meanwhile, another one ends up at the mansion and attacks the New Mutants - but Warlock takes it out.
Illyana has been delayed by the Beyonder, and turned into a complete version of herself. She takes a subway car (quite literally) to Westchester, and explains what has happened to the New Mutants, making an analogy with Clarke's Childhood's End, says that Beyonder is here to help, and is very firm indeed on the fact that she certainly hasn't been brainwashed or anything like that.
When she realises that her cleansing meant that her responsibilities as Magik devolved upon Kitty (who is now in grave risk from demons), she gives herself freely back into corruption to save her. After all, if she doesn't, she can't very well keeping calling herself good. Those Rasputins are screwed up, I tell you.