The Uncanny X-Men, Vol. 1

The alarm on Cerebro has been wailing wildly, warning of an incredibly powerful threat close by. That threat is Professor X's step-brother, Cain Marko. While he slowly penetrates the mansion's defenses, Professor X tells the story of his father's death in a nuclear accident, how his father's partner married his mother in search of her wealth and power, and how his viscious step-brother came into the picture, becoming the unstoppable Juggernaut when he found the Ruby of the Cyttorak. (Dr. Strange fans: yes, THAT Cyttorak.) Xavier completes his tale just in time for the Juggernaut to break into the mansion through all of its defenses.