The Brotherhood of Evil Mutants has freed their leader, the diabolically intelligent Magneto. An unprovoked attack on mutant-kind by a secret Sentinel army compels Magneto to plan his most maniacal scheme yet. He intends to use his mutant superpowers to shroud the Earth in cosmic debris, blotting out the sun and plunging the globe into eternal winter. From this chaos the Brotherhood will emerge to reign supreme over humankind. As the Sentinels continue to wage worldwide mutant genocide, the X-Men must confront Magneto and save the earth from certain destruction.