The X-Men hurry back to the Institute to tend to an injured Angel. Cyclops blames himself for his carelessness and feels extremely guilty. He thinks he has “failed” as a team leader because he imagines his subconscious wanted to eliminate his “rival” for the affections of Jean, whom he is in love with.
After several hours, Xavier finally emerges from his study. He informs the team that Angel will make a full recovery. However, Cerebro had detected “a new mutant menace”. The X-Men will have to face the most powerful mutant they “have ever encountered” while the team is not in full fighting force.
Meanwhile at Metro College, Jean is cheering Ted on during a track training session. She is amazed that Ted is able to perform athletically without the aid of mutant abilities. Ted tells Jean that he pushes himself because he is always being compared to his more accomplished older brother Ralph and is unable to step of out Ralph’s shadow.
Suddenly, there is an explosion in the chemistry building. Jean and Ted rush over to investigate. Calvin Rankin was involved in the explosion, and he recovered his memories that Xavier had previously blocked. He tries to get away from Jean as fast as possible. Jean suspects that Rankin had regained his “mimicking powers”.
Elsewhere, the Puppet Master is planning his revenge on the Fantastic Four. And he intends to control Xavier to make the X-Men do his bidding. Suddenly, his clay figurine becomes “charged as if with electricity” and then disintegrates. Xavier has “erected a psychic shield” against the Puppet Master’s attack. Unable to control Xavier, he seeks another candidate.
Back at the Institute, Xavier constructs a machine to boost Cerebro’s power so he is able to accurately locate the “new mutant menace”. Xavier is also suspicious about why he has not “discovered a mutant threat” as of late. He requires that he not be disturbed while his consciousness is on the Astral Plane. He goes in search of Quicksilver and Scarlet Witch and invites them to join the X-Men. The siblings turn down Xavier’s offer as they are already Avengers.
In New York City, Bobby and Hank are on dates with Zelda and Vera. A bank alarm goes off. As Bobby and Hank wonder how Iceman and Beast can leap into action without anyone noticing, they lose Zelda and Vera in the commotion. But Spiderman had already put the robbers away. Xavier contacts the X-Men and instruct them to recruit Spiderman but he is already with the Avengers.
The next day, Xavier, Scott, Hank and Bobby go to Metro college to pick Jean up for the weekend. Jean notices that Xavier is distant and preoccupied with something. (Xavier was searching for Johnny Storm on campus but could not find him.) Jean has a surprise for the team. As the X-Men prepare to leave, they are interrupted by Rankin, who wishes to come along with them. The X-Men distrust Rankin but Xavier invites him, curious to know what Rankin wants with the X-Men.
As the Puppet Master snoops on the X-Men, he comes up with a plan to use the Mimic as he has the combined powers of all the X-Men.
After spending some time with the X-Men, the Mimic regains the powers of the X-Men. He intends to “keep ’em for good”. Rankin challenges the X-Men to a sparring session. Marvel Girl reveals her surprise: new costumes for the whole team. Xavier informs the X-Men that Cyclops is to step down as “deputy leader” of the X-Men. The Mimic will be Cyclops’ replacement. The Mimic is under the impression that he will soon lead the X-Men against “an impending mutant menace”. But he is unaware that the Puppet Master intends to take advantage of his abilities. Xavier senses the Puppet Master taking psychic control over the Mimic.
The Mimic engages the X-Men in a “practice” session. During the session, Xavier tells the X-Men to not use full force while fighting the Mimic. This in turn causes the X-Men to be defeated by the Mimic. It was Xavier’s plan to have the X-Men appear to be defeated so the Puppet Master “would cease monitoring [their] every action” and they could spring an attack.
After the Mimic takes off, the X-Men go in search of the Puppet Master. The Mimic had not strayed far and follows the X-Men. Angel wants to help his team and drives off to join them despite Xavier’s pleas for him to not go into the field until he has recuperated.
The X-Men approach the Puppet Masters lair, triggering the alarm. The Puppet Master sends an android to attack the X-Men, which is quickly defeated by Cyclops blasting a hole in the floor beneath the android, causing it to fall in. They find the Puppet Master, who quickly commands the Mimic to deal with the X-Men. Cyclops wonders how the Mimic is able to retain Angel’s wings since they are far from the Institute.
Unknown to his team mates, Angel has arrived at the lair. Angel sneaks into the lair undetected and ambushes the Puppet Master from behind. He smashes the figurine of the Mimic, and then collapses from exhaustion. Though the Puppet Master escapes, the X-Men are relieved that Angel is unharmed.
The Mimic is ashamed to find out that he had been mind-controlled.