The X-Men assemble in Xavier’s study because of an emergency alarm. The professor used a new device called Radar-Image Beam to detect a powerful presence. In fact the superpowered being is too powerful and the device explodes before it can give a clear image. Hank and Bobby start to fool around showing off with their powers. Xavier interrupts and reminds them that this might be the most powerful mutant that they ever encountered.
Not far away an unusual man (he has a strange looking beard) rents a furnished room. As the landlady tells him that she expects payment for one week in advance he apologizes for being a stranger and not familiar with the customs. Then he reaches into his pocket and pulls a large pile of money from it.
Later the Stranger goes out for a walk and tries to familiarize with New York. As he gets to a crossing blocked by heavy traffic, he simply air-walks above the cars. After he becomes aware that people are staring at him, he realizes that he is causing too much of a commotion. He decides to get away. Phasing through a wall he enters a nearby building that somehow attracts him. Inside he is greeted by Magneto’s Brotherhood of Evil Mutants, the building is their new headquarters.
In the streets below the X-Men have split up and search for the new mutant. With his many questions Scott arouses the curiousity of two policemen. They ask him to take off his glasses, but Cyclops refuses. Of course that makes him even more suspicious and the policemen grab him and pull off the glasses releasing his optic beams. Luckily the Beast is near and before anyone gets hurt he pulls Scott and jumps away with him over some roofs onto an ice-slidemade by Iceman.
In Magneto’s rooms the Stranger is asked to join the Brotherhood. To impress him Magneto ties him up with some metallic cables and Mastermind casts illusions of being below the ocean and in the middle of a volcano. Annoyed the Stranger demostrates his vast abilities; with one single blast of energy he disrupts the illusions, breaks his bonds, destroys the headquarters and turns Mastermind into solid matter.
The illusionist is now too heavy and the floor gives in. Mastermind falls through the whole building, he passes through a store and lands in the cellars below. The shop owner runs out on the street and calls for help.
Nearby the X-Men hear his cries and rush to the building. Angel, Beast and Iceman are the first to arrive and enter the room through some holes in the outer wall. Magneto orders his minions to fight the X-Men while he protects himself and the Stranger with a magnetic shield.
Yet the Stranger needs no shielding and plans to depart; he turns into a small invisible vortex of air. Magneto doesn’t want the Stranger to leave and he is offered to join the Brotherhood. The Stranger disappears by simply stepping into his cone of energy. Magneto too vanishes into the vortex and the ever loyal Toad jumps after him. Then the vortex leaves the building and passes the unsuspecting Cyclops and Marvel Girl on the way.
As Jean and Scott arrive in the room they start to fight the Scarlet Witch, but she doesn’t fight back since she is only concerned about her brother’s welfare. During the battle Quicksilver had been encased in ice by Bobby and now he can’t breathe. Cyclops uses his powers to cut Pietro out of the ice-construct and thankfully the siblings announce they are leaving the Brotherhood. They only served Magneto to work off an old debt, but after so many battles they consider to be even. Cyclops asks them to join the X-Men, but the siblings refuse, wanting to return to their native country in Europe.
The Stranger’s cone of energy emerges in a wooded area. Magneto demands to know what exactly the Stranger’s mutant powers are, but the Stranger replies annoyed that he is no mutant at all. As he continues to explain that he is a stranger to the planet Earth he enlarges. Magneto judges that the Stranger is too powerful and tries to use his magnetism on the alien, but the Stranger simply encases both Magneto and the Toad in anti-magnetic membrane.
Back in Westchester Xavier examines the stone body of Mastermind. He still seems to be alive inside even though his molecules have been altered. Realizing the enormous power of the Stranger, the X-Men board a helicopter to search for him once more. Guided by Xavier the helicopter reaches the wooded area and the X-Men discover Magneto and the Toad in their cocoons.
The Stranger appears and explains that the membranes will protect the two villains for their journey through space. The Stranger‘s people are interested in mutations and so he travels from planet to planet to collect specimen. This time he was unsure about who to pick, but since Magneto insisted to ally himself with the Stranger he chose him and the Toad who was always at his side. The X-Men gaze in awe as the Stranger departs with his passengers.
Minutes later the police arrive and the X-Men hurry home to avoid their questions. Back at the mansion Xavier and Cyclops remove the names of Magneto, Toad and Mastermind from Cerebro, since these threats have finally ended. Suddenly the device starts to beep, it has detected another powerful energy signature very nearby.