Betrayed by a persecuting humanity, and in a state of emotional pain, one of Professor X's students has turned his (or her) back on the X-Men... and joins Magneto's Brotherhood! How will the remaining team members deal with this betrayal, especially if it tips the balance of power in Magneto's favor?

The Brotherhood of Mutants, led by Cyclops, bomb Britain's Parliament as a warning to Prime Minister Blair not to develop a Sentinel program. Despite Xavier's favor with the President of the United States, the Sentinels are sent on one last mission to exterminate all of Magneto's followers in the Savage Land.