Xavier has tracked down Lucifer, who cost him the use of his legs, but finds his foe's heartbeat is rigged to a giant thermal bomb. The X-Men arrive in Bavaria and run across the Avengers who have also just arrived. The X-Men have to stop the Avengers from defeating Lucifer since by defeating Lucifer, the world will be destroyed. After Xavier gives Lucifer a mind blast that renders him unconscious, he contacts his team for help and the Avengers agree to let the X-Men clean up the current crisis on their own. Cyclops uses his eye beams to disable Lucifer's thermal bomb.
in Fantastic! (IPC, 1967 series) #16 (3 June 1967) [Black and white, pages 1-11 only.], #17 (10 June 1967) [Black and white, page 12 (panels 1-3 and 5) and pages 13-20 only.]
Letters from: Paul Bakulski, Christine Austin, Donald D. Ensign, William Bailey, Kenneth S. Gallagher, Steve Chapman, Kathleen Neff, and Steve Brown; Special Announcements Section; Mighty Marvel Checklist.