Professor X gets evil and astrally starts mucking about in the Microverse. More than mucking, actually—destroying. His mighty brain crushes entire populated planets. He’s possessed by “The Entity.”
The X-Men shrink down to try to combat evil X, and they’re joined by some New Mutants as well.
Some get hijacked, with some Micronauts, by the evil X.
Fighting, etc. Day is saved.
Ultimately, this is a “doesn’t matter” comic, but it’s pretty good.