I can’t think of a five-issue arc in any modern series where more happened than these five issues–and this is pretty typical of the unrestrained, boundless creativity in these Chris Claremont/John Byrne comics.
The main story is about Mutant X, a.k.a. Proteus, who is the son of Moira MacTaggert–and the child of rape.
We don’t actually see him for most of this arc, though, because he possesses the bodies of others and alters reality.
He kills one of Madrox’s duplicates, and it appears Madrox is one of the dozens of non-member-hangers-on at this point.
The battles with the body-possessing Proteus span all of these issues, and he is ultimately defeated. First, Jean hits with psychic attacks…
Then Havok and Cyclops hit him…
And the team figures out he has a vulnerability to metal, so Colossus tricks the struggling Proteus into possessing him, turns to his metal form, and symbolically “strikes” Proteus’ non-corporeal form.
I’m saying “symbolically.” Proteus has no body, and has to jump from figure to figure. So, as soon as Colossus turns to steel, Proteus should instantly die by ceasing to exist.
While this is going on, Charles Xavier is in space with his lover, Lilandra. Moira, who is helping handle the young mutants in his absence, thinks of him as she worried about Jean Grey who appears to have found a way to put a governor on her own, ever-expanding powers.
Jason Wyngarde continues to wield power over, and forge connection to, Jean Grey.
His vision is that Jean will become Black Queen, and that will be her final transformation.
But we all know better, don’t we?