An alien race calling themselves the Kh'thon descend upon the planet, announcing that they are the former occupants and rightful owners of Earth. The evidence they present is startling: Their ships are manned by Homo sapiens, supposedly descendants of human beings who served the Kh'thon on Earth countless millennia ago. And their will is enforced by the Exemplar, humans augmented with a dizzying array of powers, each the match of any one of the X-Men. The Kh'thon claim that they are responsible for the creation of the x-gene, devised so that they could breed whatever traits or abilities they required of their servants. And now they've returned to take back what they believe is rightfully theirs: the planet Earth, and everyone living on it.

It is up to Wolverine, Kitty Pryde, Nightcrawler, and the rest of the X-Men -- working in conjunction with Scott Summers, currently a member of X-Force -- to find a way to repel the Kh'thon before humans and mutants alike are enslaved by alien masters....