Cerebro detects a powerful mutant and Xavier fears that he knows who it is. The X-Men prepare the mansion for an all-out assault. As the mysterious villain batters his way through the mansion's defenses, Professor X tells his students his origin story and how his step-brother changed from tormenting bully to an unstoppable Juggernaut.
in Fantastic! (IPC, 1967 series) #22 (15 July 1967) [Black and white, pages 1 to 11 only.], #23 (22 July 1967) [Black and white, pages 12 to 20 only, plus a new recap page.]
Letters from: Marlene Jablon, Tim Ellis, Patrick Clark, Raymon Miller, Pete von Sholly, Jonathan Singer, Marty Ross, and Walter Smith; The Mighty Marvel Checklist.