The X-Men have just learned that the Terrigen Mist-the source of the Inhumans' powers that through a cruel twist of fate is lethal to Mutants-has reached an irreversible saturation point, rendering Earth uninhabitable to their kind. And now they see no other option than to strike against the Inhumans to ensure their own survival. But one X-Man doesn't take the decision lightly. STORM has literally led the X-Men through hell and back, but will she lead them against their longtime friends and allies?