Uncanny X-Men #9

In the Northern Atlantic, a freighter is on a collision course with an iceberg. Suddenly, two red beams of light shoot out from the front of the ship and destroy the iceberg. Scott Summers and the rest of the X-Men head back to their cabin before anyone can see where the strange light came from. The X-Men attend to Scott who became weary after having to use his powers so rigorously. Scott explains to the other X-Men that Professor Xavier had told him they had a mission in Europe.

Suddenly another transmission from Professor Xavier comes in, telling his students that he has located his foe, Lucifer in a cave in the Balkans. He tells the X-Men that he wants them to come to the cave. If he is unable to stop Lucifer, they can finish him off. Professor Xavier enters the cave, but is engulfed by a cyclone that places him in front of Lucifer. Professor Xavier pulls a gun on Lucifer, but learns that if he pulls the trigger the world will be doomed.

The X-Men arrive in a Bavarian village. The Avengers arrive just behind them because they are investigating strange impulses detected by Thor's hammer. Lucifer reveals to Professor Xavier that he has built a thermal detonator attached to his heartbeat. If he is harmed or killed, it will blow up, causing worldwide damage. Lucifer knows that the X-Men have arrived in Europe, so he fires an ionic ray at them. Professor Xavier warns his students of the incoming ray, and they dodge it. He tells the X-Men of Lucifer's bomb, and that Lucifer cannot be harmed. The Avengers arrive and want to destroy the menace detected by Thor's hammer. A battle between the two groups ensues.

Lucifer laughs after seeing the two groups fighting each other. Professor Xavier uses the distraction to mentally knock Lucifer unconscious without changing his heartbeat, and then using telepathy, alerts Thor to the truth. Thor informs the rest of the Avengers of Lucifer's defeat, and they depart.

Professor Xavier leads the X-Men to him so they can defuse the bomb. He detects the bomb's weak point and orders Cyclops to use his power full force but in a hairline beam on the bomb's fuse, shattering it. The bomb is diffused and Xavier mentally wakes up Lucifer. Lucifer tells them that it took him 10 years to make the bomb, and Xavier says that he lost the permanent use of his legs, but Lucifer only suffered a minor setback. The X-Men leave Lucifer alone in his own cave, telling him that there is no place on Earth he can go to escape the retribution of the X-Men.