Professor X reveals something about his past as a child: after the death of his father during a nuclear accident in Alamagordo, Dr. Kurt Marko (a friend of his father) married Xavier's mother ( Sharon) to help raise him, and to take control of Xavier's money. Dr. Marko had already a boy, Cain Marko, an evil boy that always bullies Xavier. When Xavier discover his mental powers he becomes very good in everything, from classes to sports because of his powers. Cain was always jealous about Xavier. Years later, during the Korean War, the two brothers were together for the last time, when Cain entered a cave and found a gem ( Crimson Gem of Cyttorak) that morphs himself into the Juggernaut.
Meanwhile the story has been told by Xavier to his students, the X-Men are preparing defenses inside the X-Mansion. The Juggernaut is approuching and easily destroying every defense armed by the X-Men. Suddenly, the Juggernaut finally enters the mansion and the room where the X-Men are.
This is the first story with Xavier's mother, Kurt Marko and Xavier's stepbrother, the Juggernaut.