In exchange for protection against her countless enemies, Mystique reluctantly agrees to work for Professor X, but only as a secret agent whose operations can't be traced back to Xavier or the X-Men. Can this former mutant rights terrorist, who can disguise herself as anyone on the planet, be trusted?

Professor Xavier, the mentor of the X-Men is forced to confront his past sins when his own son explodes into a destructive force, and Jean Grey turns to the dark side, forcing the team to strike down one of their own in order to save themselves and the world. The death of one of their own leaves the remaining X-Men struggling to deal with the loss. And even before a moment of silence can pass, the mysterious Mr. Sinister arrives, intent on giving...