New X-men by Grant Morrison 1 (X-Men, 1)

As protesters lay siege to the Xavier Institute, mutant mentor Professor X lies in a coma - dying, trapped within the shattered form of his evil twin! Cassandra Nova inhabited Xavier's body and escaped to the stars in the wake of her initial encounter with the X-Men; now, the psionically empowered psychopath is returning to Earth - possessed of the most powerful mutant mind on the planet, and with the might of the Shi'ar Imperium at her back! She brought an interstellar empire to its knees. Can even the X-Men hope to halt her mad rampage? Collecting NEW X-MEN (2001) #122-126.