The Terrigen that grants the Inhumans their powers has been released into Earth's atmosphere. But while the Terrigen Mists circling the planet are creating ever more new Inhumans, mutants are dying from exposure to the substance. Both groups have sought a solution to the problem and a fragile truce has held, until now. Brilliant scientist and longtime X-Man Hank McCoy, the Beast, has discovered the terrible truth: soon, there will be nowhere left to hide from the poisonous gas. Mutantkind's days are numbered, unless the Terrigen can be destroyed. And if that happens, the Inhumans' legacy will come to an end. There are no options left. This means war.