The Inhumans release the Terrigen Mists in order to awaken the Inhumans on Earth.  Only problem, it's deadly to mutants and, thanks to an attack from Magneto and lies from Maximus, the Inhumans don't know what they've done.  So now the mutants and Inhumans are at war and Maximus is organizing a rebellion.

Note: This takes place after the X-Men, Attilan and Namor RP but does not have to be played before this.