In the North Atlantic a superliner is about to hit an iceberg, but suddenly two beams of red energy shatter the iceberg apart. On board of the freighter are the X-Men in civilian clothes and as all passengers were looking at the danger ahead nobody saw who shot the beams.
Still this powerful blast took a lot out of Cyclops and his teammates take him to their cabin to rest. Iceman creates some ice-cubes that Jean uses to telekinetically cool Scott’s brow. She again thinks that she can’t reveal her feelings for Scott since he as leader has no time for romance.
Feeling better, Cyclops explains that he was contacted by Professor Xavier recently and that he wanted them to come to Europe, as a second transmission from Xavier comes in. The professor has located his foe Lucifer in some hidden caves in the Balkan. He tells his students that it was Lucifer who cost him the use of his legs years ago and he wants his X-Men to follow him, just in case that he himself fails to defeat Lucifer.
The mental contact ends and Xavier uses his vehicle to venture deeper into the caves as a mini cyclone appears that carries Xavier right into the base of Lucifer. Face to face with his foe, Xavier pulls a gun, but Lucifer warns him that if he were harmed the world would be doomed.
Meanwhile the X-Men arrive in a Bavarian village. Not far away another superteam from the US is seen – the Avengers. They are investigating strange vibrations of pure evil that were picked up by Thor’s hammer.
Below in the caves Lucifer reveals that he has built a giant thermal bomb that is attached to his heartbeat, should he be harmed the device will blow up causing worldwide damages. Also he knows that Xavier’s students have followed their mentor to Europe and he fires an ionic ray at the surface. Fortunately Xavier can alert the X-Men through his telepathy and the team evades the deadly bolt.
Xavier warns his students that no physical harm mustbe done to Lucifer since that might set off the bomb. Suddenly the Avengers arrive still following the evil emanations picked up by Thor’s hammer. They intend to investigate and do not listen as Cyclops tries to explain what transpired and so the X-Men have no other choice than to fight the other hero team to prevent them from finding Lucifer.
In the caves below Lucifer laughs as he sees the hero teams fighting each other. This short distraction gives Xavier the opening he was waiting for. He uses his telepathic power to render his opponent unconscious yet without affecting his heartbeat in any way. Having defeated his archenemy, Xavier telepathically contacts Thor and explains to him why his students were forced to fight the Avengers. The Thunder God fills in his comrades and as the real enemy is already beaten the Avengers leave.
Guided by Xavier, the X-Men enter the caves and come to Lucifer’s base. Once there they have still to defuse the bomb, Xavier detects its weak point and orders Cyclops to use his optic beam full force yet only narrowed to a hairline.
With the explosive mechanism destroyed, the danger has passed. Lucifer wakes up, it took him ten years to build that bomb and now Lucifer believes to be even with Xavier, but the Professor complies that the damage to his legs is permanent while Lucifer only has to face a major set-back. Having intervened with their foe’s deadly plans, the X-Men let Lucifer go since they can not punish him anymore.