The X-Men are taking a cruise down the Rhine in Germany when Jean senses a bomb in the water. Scott manages to blast the bomb away as it detonates. The explosion almost causes damage to the boat. Professor Xavier maintains a psychic link with his X-Men as he explores an underground cavern in Cologne, Germany.
The previous day, Professor Xavier announces to his young field leader, Cyclops, that he would be taking a leave of absence to fight an enemy, leaving Cyclops temporarily in-charge. The X-Men will accompany him to Germany, but Xavier will only call on them if they are needed. Cyclops is furious that the professor will not disclose all the facts regarding his personal mission.
Back on the cruise ship, Scott is having a headache from exerting his powers. Jean attends to him with an ice pack provided by Bobby. Scott is clearly bothered by Xavier’s secret mission. Just then, Xavier summons the X-Men. He is about to battle an alien and old enemy known as Lucifer, and he wants the X-Men to protect him from outside interference. Should Xavier be defeated, the X-Men have to stop Lucifer. Xavier is teleported into Lucifer’s lair.
The X-Men take to the streets of Cologne. In a distance, they spot the Avengers arriving in their jet.
Meanwhile, Lucifer exposes his plan to Xavier. Should Xavier open fire on him, all the electronic equipment on Earth will be destroyed. Xavier warns the X-Men to “scatter” as they are in danger. The X-Men narrowly miss an explosion intended for them. They turn off their image inducers to reveal them in X-Men garb.
The X-Men are confronted by the Avengers. The Avengers intentions are unknown, and the X-Men carry out Xavier’s orders to ensure that the Avengers do not disturb Xavier. They immediately jump into battle with the Avengers. But the Avengers prove to be too strong for the X-Men to handle.
Xavier realised that he had made a rash decision to ask the X-Men to battle the Avengers, but he has other pressing issues to defend himself and the world from Lucifer. Xavier stuns Lucifer and calls out to his X-Men and the Avengers. He explains to the Avengers that the X-Men were merely distracting them to buy him time needed to battle Lucifer. The Avengers are regretful that they have acted hastily, and leave the X-Men to go to their professor’s aid.
With the help of Cyclops, Xavier and the X-Men have saved the day again.