Taking a different approach to his research, Jeremie materializes a single hair of Aelita's. Unfortunately, the follow-up test goes awry, and Jeremie has to find out why. Meanwhile, different parts of the school begin to crumble apart. Jeremie learns that his first test damaged Aelita's program as he pressed a button he shouldn't have while coding, and she'll be deleted if she tries to deactivate a tower, so the two attempt to debug the code before X.A.N.A attacks again.
On top of that, they learn that X.A.N.A. is responsible for the damage being caused to the school by using ultrasonic sound waves, which continues to get worse. Jeremie has to fix the damage he caused in time to save Odd, who ends up trapped in the school with Milly, Tamiya and Kiwi.
Unfortunately, after two tries, both ending in failure, Aelita has to deactivate the tower or else Odd, Milly, Tamiya, and Kiwi will be done for. After the return back in time, Yumi remembers that Jeremie said that the hair contained Aelita's entire computer code. So, Jeremie places the hair in the scanner, virtualizes it to Lyoko and Aelita reappears inside a random tower in the Desert Sector.
This episode contains examples of:
- A Glass in the Hand: When Sissi threatens to expose Kiwi to the school, Yumi threatens her in return and, barely squeezing the glass cup in her hand, it shatters. Everyone is surprised and Sissi, taking it as a genuine threat, backs off and simply leaves.
- Big "NO!": Jeremie shouts one after Aelita gives him a fond farewell, as well as shouting her name.
- Brick Joke: During lunch, Ulrich complains about Kiwi's shedding over his bed, and later when X.A.N.A. makes his first move, Jim tells the boy to clear his sleeping area of all that hair.
- Chekhov's Gun: The single strand of hair of Aelita that Jeremie materializes at the start of the episode plays a vital role at the end where it saves Aelita from being lost forever after saving the day.
- Cover Innocent Eyes and Ears: A computer variation where Jeremie swivels the monitor around so Aelita can't see his boxers that Kiwi is chewing up just out of frame. Though she does attempt to "see" what the commotion is about.
- Evil-Detecting Dog: Kiwi, accidentally, as he is the first to notice the problem. Ulrich and Odd theorize that Kiwi can hear the sounds, so he comes off as noticing the issue first. Yumi also notices the dogs in the town on her way to the factory howling at the ultrasonic sound.
- Extreme Omnivore: Kiwi stays with Jeremie temporarily in an effort to stop him from getting rumbled, though all this does is have Kiwi start chewing at his slipper, and then later Jeremie's boxers, which embarrasses Jeremie enough to turn the monitor sideways on Aelita so she can't see them, retrieve them and put them away, and claims that it was a handkerchief.
- Heroic Sacrifice: Aelita deletes herself to stop XANA, despite Jeremie's pleas. Fortunately, Yumi realizes that the hair can be used to "reboot" her program and restore her.
- Hollywood Hacking: Subverted, Jeremie knows debugging Aelita's code is gonna take a while, so he asks Ulrich and Yumi to cover for him, and he's still working on it up until XANA attacks.
- Make Some Noise: X.A.N.A.'s plan involves using ultrasonic soundwaves to destroy the school.
- Manly Tears: Jeremie cries some when he sees Aelita alive again. She takes note of the "Water on [his] face", but he says he'll explain that at a later time.
- Title Drop: Yumi breathes "Just in time, too, things were getting a little hot around here" when Jeremie announces a Hope Spot.
