The tragic death of a student at the Xavier Institute reveals that a powerful enemy is working from inside the mansion to destroy the X-Men, an enemy who knows all their weaknesses and can predict their every move. This new foe doesn’t want wealth, power or world domination: it only wants them dead. As the X-Men fight for their lives, they learn they’ve been deceived by one of their own... even if they survive, the team will never be the same.