Cyclops is put in charge of overseeing the X-Men’s training sessions. The session is going smoothly, until Angel accidentally messes up Iceman’s target practice. In childish retaliation, Iceman “toss[es] a mess of ice flakes” in Angel’s face. Cyclops quickly puts an end to the brawl between his two team mates.
The training resumes with Beast attempting to “beat [his] own speed record on the trapdoor obstacle course”. Beast is unaware that the timing of the course has been altered. In showing off that he can achieve the task balancing on one hand, the weighted obstacle thrown at him caught him off guard, and he flings it hard into the path of Angel and Marvel Girl. Marvel Girl telekinetically deflects it and Cyclops uses his optic blasts to slow the weight down. Professor Xavier ends the session with an “announcement”.
Professor Xavier has decided that the X-Men deserve “a little vacation”. Iceman and Beast race off on their double-date with Zelda and her friend. Marvel Girl plans to spend the day shopping. Angel asks Cyclops if he would like to go on a “double-date”. Cyclops politely declines. He is secretly in love with Marvel Girl but does not dare to ask her out.
Cyclops: “If only I dared to ask Jean for a date--! But, I haven’t the right--so long as my power beam is an ever-present danger!”
Bobby and Hank arrive early at the library to meet Zelda and her friend. While looking at some books, the librarian tells Hank that he might find those books too juvenile as they are for children. Hank argues with her that it is his right to look at whatever books he wants. Bobby notices that Zelda has arrived alone. Zelda then introduces Bobby and Hank to her friend Vera, the librarian.
The four of them leave the library. On the street, they meet Calvin Rankin. Vera has previously turned down Rankin’s advances, and he is upset to see her on a date with Hank. Rankin angrily approaches Vera. Hank steps in. Rankin throws a punch at Hank but Hank quickly “dodge[s]”. Rankin could not believe that he missed Hank, and starts a brawl. Soon, Hank discovers that Rankin has mysteriously inherited his powers. Hank refrains from using his powers to hide his identity. He is thus defeated by Rankin.
Bobby is upset and throws a snowball in Rankin’s face. From a distance, some construction workers witness the brawl and thought Rankin was a mutant bullying two kids. They rush over to chase Rankin away. Rankin unconsciously throws up an “ice shield” to protect him from the bricks thrown at him. He then escapes by climbing up the side of a building.
Rankin realises that Hank and Bobby are Beast and Iceman of the X-Men. He is now on a mission to find the rest of the X-Men and destroy them. But Rankin soon depletes his powers and he needs to “regain those powers--and more to carry out [his] plan”.
While getting a drink at a cafe, Rankin bumps into Jean. As he levitates the sugar cup over to his table, he realises that Jean is Marvel Girl. He plans to follow her so she will lead him to the rest of the X-Men.
The next day, Hank tells Professor Xavier about his encounter with Rankin. Xavier is astounded because Cerebro does not register Rankin as a mutant, and wants to know Rankin’s secret. Just then, the doorbell rings. Hank answers the door and invites Rankin in.
Rankin introduces himself to the X-Men, and secretly acquires their powers. Xavier telepathically tells the X-Men to “play along with [Rankin]--act as though [they] trust him--until [they] learn the extent of his power ”.
Professor Xavier lets Rankin retire upstairs in a guest room. Meanwhile, he urges the X-Men to change into their costumes and prepare to battle Rankin. When Rankin returns, the X-Men are terrified at the sight of Rankin, “a combination of all of [them]”. Rankin, now calling himself the Mimic, came here with the intention of fighting and defeating all the X-Men.
The Mimic easily takes on the X-Men individually. Xavier commands the X-Men to use teamwork to defeat the Mimic. Still, the Mimic is able to outsmart them. Though the X-Men take down the Mimic for a minute, he quickly recovers and kidnaps Marvel Girl. The Mimic intends to use Marvel Girl as bait to lure the X-Men to his lair.
The Mimic takes Marvel Girl to an abandoned mine where she is surprised to see a comfortably furnished hideout. The Mimic tells Marvel Girl his story: His father was a scientist carrying out dangerous experiments at home. He got curious and snuck into the lab one day, but accidentally “knocked over a beaker ” and the room filled with a mysterious gas. He cleaned up the mess and kept the accident a secret. Soon, he discovered that he is able to copy the skills of everyone around him. He became the smartest and most talented athlete at school. Eventually his father found out what happened and hid him in the mine for his safety. His father worked on a machine to “make [Rankin ’s] power last forever”. But an angry mob finds their hideout and Rankin’s father dies in an explosion. The Mimic sought revenge for his father’s death ever since.
Marvel Girl infers that the Mimic wants the X-Men to get the machine for him that got buried in the explosion. As the X-Men get closer, the Mimic’s powers get stronger, and he is able to get to his machine by using his acquired powers. The X-Men are too late to stop the Mimic from activating the machine. The Mimic easily takes down the X-Men and captures Xavier.
The Mimic steps into the machine but suddenly collapses. The X-Men hurry out of the cave with Xavier and the Mimic before it explodes. Unfortunately for the Mimic, his father meant to “take those powers away”. Now Rankin is free to led a normal life, having no memory of all that transpired thanks to Xavier erasing his memories.