Professor X gets evil and astrally starts mucking about in the Microverse. More than mucking, actually—destroying. His mighty brain crushes entire populated planets.
The X-Men shrink down to try to combat evil X, and they’re joined by some New Mutants as well.
Ultimately, this is a “doesn’t matter” comic, but it’s pretty good.
Creators: Chris Claremont, Bill Mantlo, and Butch Guice