The X-Men barely survive their return trip from space, Jean Grey discovering herself changed by the experience. Professor Xavier's dark half is given form, and proceeds to attack his students.

Professor Xavier's claims of the capture of his alien soulmate Lilandra by Juggernaut and Black Tom Cassidy are met with skepticism.

Snatched from the jaws of the Phalanx by the villainous Mr. Sinister, Beast and Forge search for allies to help them battle the alien threat. Gathering assistance from such unlikely sources as Magneto and Sinister himself, they embark upon a daring and risky plan to free the planet from the clutches of the Phalanx by traveling straight into the belly of the beast.