The X-Men are in the Danger Room wh practicing their skills. Iceman is throwing icespears, Jean is levitating herself while reading a book. Beast is balancing a large ball with his feet and the Angel is diving through the air; all under supervision of Scott. As always the team is fooling around with each other until the professor calls them. After fighting the Sentinels and Magneto, he thinks the team has earned themselves a vacation. The team is quite happy and start to make plans, only Scott is brooding, he would like to ask Jean for a date but doesn‘t dare.
Later, Bobby and Hank go to the library where they are to meet with Zelda and a blind date for Hank. In the library, Hank has a short argument with the librarian, who tells him that the books he is looking at are for pre-school age children. Hank in turn says that it is the right of every citizen to chose whichever book he likes and they are still arguing when Zelda arrives. They then learn that Hank's blind date is actually the librarian, whose name is Vera. Hank blushes.
As the four of them move out they run into a character named Calvin Rankin, someone Vera knows, and he doesn't like it that Vera is dating Hank. Calvin is very hot-tempered and tries to strike Hank, but naturally Hank is able to dodge him. But when Hank tries to return the blow to Calvin he notices that Calvin is just as agile as himself. Not only that but Calvin then starts leaping around in the same way as Beast usually does.
As Bobby comes to Hank's aid, Calvin suddenly throws ice towards Bobby, just as Iceman would've done. When a group of construction workers see Calvin Rankin assault Hank and Bobby they suspect him to be a mutant and the group move towards him, forcing Calvin to flee by climbing a building in Beast-style.
At the top of the building Calvin ponders why the group of construction workers called him a mutant and then he realises he has the ability to create ice and leap around like the some of the X-Men do. t Calvin has the power to 'mimick' peoples powers and when he realises that he discovered the secret identities of two of the X-Men, he decides to follow them, hoping he can find the other X-Men as well so he can mimick the powers of all the X-Men and then destroy them. Unfortunately for him, in his excitement he forgot that he can only mimick others when they are in close range, so he lost track of Beast and Iceman.
Later Jean is doing some shopping when she suddenly bumps into someone in a restaurant. Theperson yelling at Jean is once again Calvin Rankin. When he sits down at a table he once again gets a temper when he doesn't see any sugar on his table. He wonders why it couldn't have been on his table, and suddenly the pot floats through the air towards him. Calvin understands that he just gained telekinesis, the redhead he bumped into has to be Marvel Girl. Calvin thinks that she will lead him to the other X-Men.
(the next day)
The X-Men are discussing what happened the previous day with Hank and Bobby when suddenly the bell rings. The professor knows that its Calvin Rankin who is at the door, even though Cerebro didn't show an alarm. Xavier sends Hank to open the door and let Calvin in.
He apologizes for his behavior and asks to join the team. As Rankin appears in frontof the professor, Xavier notices he is unable to probe Calvin's mind, so he has already mimicked his power of telepathy. The professor doesn't trust Calvin but he wants to play the game along until he learned the extend of Calvin's power. The professor gives Calvin permission to go upstairs where he can change clothers.
Calvin was prepared and made himself a special costume to anticipate the powers of Cyclops, Beast and the Angel. Once he is done he goes back downstairs and the X-Men are waiting for himin their costumes themselves. They learn that by now Calvin has mimicked all their powers.
Calvin, calling himself 'the Mimic', starts a battle and Angel is the first one to fall in the air. The Iceman and Cyclops try to take the Mimic out with an ice javelin and an optic beam, but he blocks the beam with an iceshield and blasts the ice javelin with his own optic beam. The professor says they must attack the Mimic as a team but when they charge at him, they suddenly get a mental message to look behind them. They assume it was the professor, but the Mimic tricked them, they had forgotten that he also mimicked the professor's powers. Eventually they manage to take down the Mimic by working as a team, but then he suddenly grabs Jean and takes her hostage. He runs away with Jean and telepathically orders the X-Men not to follow.
The Mimic takes Jean to some mine. Along the way he loses the powers copied from the male X-Men, but he has tied up Jean. Once inside, Jean is surprised as she sees living quarters in the mine. Jean says that the X-Men will find them, but that is exactly what the Mimic wants. Calvin then starts talking about his past.
When Calvin was a young boy, his father was a scientist. One day his father was on an arrand and out of curiosity the boy entered his father's lab and knocked over a beaker with chemicals. A aas filled the room and Calvin breathed it in.
In the years that followed strange things happened to Calvin. He was always the best of everyone, the best athlete, always as good as the teachers. All this made Calvin a very arrogant person whiched caused a lot of dislike among his fellow students. Once his father realised what had happened to Calvin, he created a secret living quarters in an abandoned mine to protect his son since he predicted that one day the people who distrusted his son would turn against them.
Calvin's skills were always only temporary and faded when the people he mimicked were no longer near, so his father came up with an idea to make the powers his son mimicked permanent. The creation of this machine took a lot of energy so one day the machine draw so much current that every fuse in the county blew up. Eventually the people traced the source of this energy drain and an angry mob approached the mine.
Calvin's father wanted to blow up the entrance of the mine with explosives but he underestimated the force of the blast and he was killed in the explosion. After the crowd left, Calvin dug himself out of the rubble and swore revenge for the death of his father and he planned to finish the machine himself.
Jean realizes that Calvin wants the X-Men to follow to the mine so that he can gain their powers permanently. The machine that his father built is covered by rocks. He needs the powers of the professor and Cyclops to locate and free the machine.
Calvin can tell that the X-Men are close by when wings start to spout on his back. He leaves Jean in the room, while he heads deeper inside the mine to blast a way towards the machine.
While the Mimic is busy starting the machine the X-Men are freeing Jean. The team quickly goes after Calvin and a fight starts. Calvin grabs the professor as a hostage and the professor tells the team to back off, saying the Mimic can't win and that they should trust him. As the Mimic pulls the lever of the machine he suddenly collapses. The professor warns the team that the machine is going to explode and the team quickly moves out with the unconscious Calvin.
Once they are safe from the explosion Xavier starts explaining what happened. Calvin's father knew that the power to mimic people would eventually cause problems to his son, so instead of making a machine that would make his son's power permanent, he designed it to completely remove the mimicking powers, but his son didn't know about this. He still thought the machine would make him all powerful. Now that Calvin is once again a normal human, the professor removes Calvin's memory about all that happened in the past few days and they let him go.