A high school dance. A girl is seen standing by herself outside looking over a bayou, while music is heard within. Cody and his friend, both wearing football jackets, walk outside and notice her. Cody's friend teases him for not doing anything about this girl who he's been "staring at all week". Cody's friend pushes him towards her, and Cody haltingly asks her to dance. She starts to blow him off, but then agrees saying, "After all, what's the harm in one dance?" Cody high fives his friend as the three walk back indoors.Irene, a blind woman, is seen sitting in her home. Behind her a photograph is framed on the wall showing her, another woman, and a child. Irene suddenly has a vision and cries out, "No! Don't touch him!"

Back at the dance, Cody and the girl are dancing. Cody's friend pushes him closer to her, and he accidentally knocks her to the ground. Cody reaches down to help her up and accidentally touches her wrist. Unknowingly the girl drains his lifeforce, and he passes out. Images flood her mind: a blonde boy climbing a tree; the boy, now older, walking through a school cafeteria; the boy on a football field. Confused as to what has just happened, the girl stammers, "What am I? WHO am I?"
People crowd around Cody and the girl. Cody's friend shakes Cody, and then turns and angrily asks the girl what she has done. Confused, the girl runs for the door. Cody's friend runs to block the exit, but she has a flash of an image of Cody on a football field pushing past another player, and shoves him aside and to the ground. Cody's friend gets up, stunned, and says he thought only Cody had moves like that.

Irene is on the phone. She explains that she couldn't predict the exact moment the girl's powers would manifest, but that she had taken precautions by making up a phony skin condition and having the girl dress a certain way. We see photographs of the two on a table. Irene says that she knows the person she's talking to is coming, and that Xavier's team is coming as well.

Wolverine has just broken into the Institute by getting past the autodefenses by going through the air vents. Storm tries to knock him down with a gust of wind, but he escapes through another vent. She summons a storm to flush him out and into the Danger Room. She ices him against a wall, but he breaks free. She then proceeds to set the Danger Room against him, and he fights until Professor X tells him to stop because "That's as much as we can afford." Wolverine replies that "when I give a demo, I give a demo."
The four students (Scott, Jean, Kurt, and Kitty) have been watching in the control booth. Storm tells them that this was to demonstrate finding the weak points in sophisticated security systems. The two adults discuss improving the defense on the vents. Kitty is freaked out by Wolverine's talk of electrified fences and poison gas and Kurt's teasing and teleporting, and exits via the floor. The Professor enters and tells them that they have a mission: to find the new mutant in Mississippi. We see the girl pushing through people and running in the streets, causing a car to narrowly miss her.

Kurt is piloting the Blackbird as Cyclops coaches him. Kitty talks to Jean about how impressed she is with Scott, and Jean says he's "stiff" and "exacting", but that "from a certain angle ..." Kurt, overhearing the conversation, teleports outside onto the front of the Blackbird in an obvious effort to impress Kitty. It backfires, though, when he stumbles, and, teleporting back inside, stumbles against her. Another plane is seen landing and Raven Darkholme exits and enters a car where Irene is waiting. Darkholme transforms herself to Mystique as Irene explains what happened. Mystique says they put the girl there for the past five years to keep her safe, and that they cannot lose her, especially not to the X-Men, and that the girl has the potential for "limitless power". Irene tells Mystique that the girl will go to what she thinks is her home.

The girl walks up to a house and has an image of a man, her father ostensibly, greeting her. She reaches for the key, which she somehow knows is hidden on the low-hanging roof, and enters.

Meanwhile the Professor has sent Jean inside the hospital to form a link between Cody and the Professor's minds. What he sees in Cody's mind surprises him.

Irene and Mystique arrive at Cody's place. Irene asks Mystique not to hurt her, because after all she's Mystique's ... Mystique interrupts and says, as she shifts to look like Wolverine, that the girl will come with them "given the right incentive."

The girl is in Cody's room looking through his photo album which contains football pictures. She's confused that this blonde football player is her. Frustrated, she knocks Cody's trophies off of his dresser. "Wolverine" barges in and threatens the girl, and says that he's one of the X-Men. The girl escapes and as "he" follows, Mystique changes herself to look like Storm.

Wolverine, Shadowcat, and Nightcrawler are searching for signs of the girl because the Professor has said that the girl is difficult for him to find. Suddenly Wolverine catches a scent.

Mystique, as Storm, throws a device towards the girl, which flashes to look like a lightning bolt. The girl runs and falls at Irene's feet. Irene tries to get the girl to recognize her, and tells her that the X-Men are mutant hunters and that Irene can take her to a safe place. Just then the three X-Men who had been looking for her appear. The girl sees Wolverine and freaks and runs off, accidentally leaving her glove in Irene's hand. Nightcrawler realizes that the girl is freaked by Wolverine, so he and Shadowcat follow her (with Nightcrawler using his image inducer) while Wolverine goes back to the Professor.
Nightcrawler tries to talk to the girl, and just when he's making progress Shadowcat tackles her. The girl has a flash of memory of Cody wrestling, and she easily shrugs herself out of Shadowcat's hold. Nightcrawler makes a grab for her and in the struggle the girl hits his image inducer. She becomes even more freaked when she sees Nightcrawler's true form, and pushes against him, accidentally absorbing his powers and teleporting away. Shadowcat tries to get Nightcrawler to wake, but without success.

The girl has teleported to a cemetery. She is confused and realizes that she can speak German, and that somehow she has become like Kurt, just like she had become Cody. She finally understands her power, and then she experiments with teleporting. Just as she's beginning to enjoy teleporting she lands with a bump and wonders when it's all going to end.

Kitty, upset that Kurt is out cold, tries to contact the Professor. The Professor is with Cyclops, Jean, and Storm. He is puzzled because Cody's brainwave patterns have suddenly gone cold. He believes that the effect of transference must be temporary. Wolverine arrives and gives him a quick update. Kitty contacts the Professor and tells him what has happened. The Professor sends the others ahead to look for the girl.

Mystique sees the girl sitting in the cemetery. Jean approaches the girl and the girl sorts through Kurt's memories and realizes that she's Jean Grey and one of the X-Men. Jean calms her and gives her a communicator, just as Cyclops and Storm walk up. When the girl sees Storm she freaks out and runs off again. Mystique gets an idea of how she can put up even more blocks between the girl and the X-Men.

Kurt is still out. Kitty is upset about the way she had treated him before talks to him although he's unconscious. Mystique, disguised as Cyclops now, finds the girl and intimidates her.
The girl runs and bumps into the real Cyclops, and shoves him. Surprised, he accidentally shoots a beam and hits an electric tower. Mystique, appearing as Jean Grey, threatens the girl, and she teleports away and falls. The real Jean Grey tries to help her but the girl backs away and accidentally absorbs Storm's powers. The girl unleashes a furious, uncontrolled storm. She causes trees to uproot and parts of the cemetery to collapse. A lightning bolt hits a power line, and Cyclops and Jean rush to pull Storm from a pool of water just as the power line hits it. The girl is unable to control the storm. She gives a scream and teleports away, and the storm quickly dissipates.
The X-Men regroup. The Professor says he's unable to find the girl, and that he suspects someone else was involved. Wolverine says it was Mystique, and the Professor decides that enough damage has been done for one day and that the girl must come of her own free will. Storm and Nightcrawler revive. Kitty is particularly excited that Nightcrawler is okay, much to the surprise of Cyclops.

Next Day. Cody has recovered as well, and in the window of the hospital we see the Blackbird on its way home.

Principal Darkholme welcomes the girl to Bayville High. After she exits Magneto tells Mystique that the girl is a powerful addition to their side. He asks her if she's sure that any memories of the true X-Men have faded, and Mystique says she's positive. But as Rogue walks through the school she pulls out the communicator Jean gave her and looks at it.