I can’t think of a five-issue arc in any modern series where more happened than in 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 never actually see him, though, because he possesses the bodies of others and alters reality.
But the more interesting story is the further development of Jason Wyngarde, who reveals his power over, and 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?