Magneto--the X-Men's oldest, deadliest foe--has taken over a top-secret government installation that houses the Sentinels, powerful mutant-hunting robots. The X-Men must fight to keep this deadly technology out of Magneto's hands and stop him from carrying out his grand plan: establishing a global Mutant Empire. The X-Men must join forces with old enemies to stop him--but in Magneto's brave new world, who can they trust?