After an unexplained incident on Lyoko ends up devirtualizing Yumi without any cause, Yumi is taken to the infirmary. After waking up, she attacks the school nurse. She continues to act weird throughout the day, wanting to go to Lyoko with everyone else. Jeremie won't let them, though, because he wants to know just what caused Yumi's devirtualization.
Meanwhile, on Lyoko, Aelita finds several Kankrelats guarding an orange sphere, which she calls a Guardian, and informs Jeremie.
Back at the school, the principal confronts Yumi about her attack on Yolande. When he threatens to call her parents, she attacks him too. In another attempt to get the group to Lyoko, Yumi tries to seduce Jeremie to convince him to arrange a mission. She fails, but Odd and Ulrich stumble upon the scene. Jeremie tries to explain, leaving Yumi alone. Jeremie apologizes for the incident, citing Yumi's strange behavior. When they head back to his room, they find his computer destroyed. Yumi seems the likely culprit. She shows up to meet them, still wanting to go to Lyoko. Having no choice, they go, but Yumi stops the scanner before it can close, leaving her alone in the scanner room. As she goes to work destroying the scanners, the others find the real Yumi trapped inside the Guardian.
In Lyoko, Aelita figures out a way to defeat the Guardian. She creates a clone of Yumi via her Creativity. The Guardian gets confused and tries to absorb the clone Yumi too, but this is beyond its ability and it explodes in a brilliant flash, releasing Yumi.
Yumi volunteers to return to the Factory, but Ulrich points out that without Jeremie, they can't be devirtualize. Yumi tells him "You're armed, aren't you?".
The real Yumi emerges from the Scanner (it is implied that Ulrich must have devirtualized her with his Katana, but this is not seen.) She and X.A.N.A.-Yumi fight each other.
Jeremie wakes up, but the hatch leading to the Supercomputer Room was torn off by the X.A.N.A.-Yumi. Jeremie pushes X.A.N.A.-Yumi into the hole. However, she grabs Jeremie and tries to throw him in. Aelita deactivates the activated Tower, killing X.A.N.A.-Yumi and making her vanish (this is not seen). Then, a time reversion envelops everything, saving Jeremie from certain death.
Back in the past, the real Yumi pretends to seduce Jeremie again as a joke, but Ulrich stops her.
This episode contains examples of:
- Almost Kiss: Between a clone of Yumi and Jeremie. This was done by XANA to break the team up from the inside.
- Ambiguous Situation: Regarding Clone Yumi; was it X.A.N.A. himself taking her form, or a polymorphic clone that still had kinks to be worked out? Given the Early-Installment Weirdness of Season One combined with what we see demonstrated from said later clones, it is difficult to say.
- Big "NO!": Yumi screams this when her evil imposter is about to throw Jeremie into the hatch in an attempt to murder him, but was too injured to stop her. But luckily Aelita reversed Just in Time.
- Blowing a Raspberry: Odd blows a tiny one to Jeremie in Mrs. Hertz's class after his, ahem, rendevous with the Yumi clone.
- Confronting Your Imposter: Yumi insists on doing so, a potential mistake, as she can't outfight the duplicate very well. Though considering none of the others have shown to be good at fighting anywhere but Lyoko prior to this episode, it's possible neither Odd nor Ulrich would've stood much of a chance either.
- Curb-Stomp Battle: Yumi's idea of confronting her evil clone almost immediately blows up in her face, getting decked by Evil!Yumi pretty easily.
- Devil in Plain Sight: More than likely, most viewers figured out something was wrong with Yumi before the show told them.
- Does This Remind You of Anything?: "Take me to the scanner room" is very clearly a G-rated "Take me somewhere we can make love" proposition. Fake Yumi's actual intent was to break the group up and destroy the scanners, and a good way of doing that was to get Jeremie alone.
- Early-Installment Weirdness: Combined with Dub Name Change; Yolanda is called Dorothy in the English version before Season Two would revert it back to her original name.
- Assuming that Clone Yumi is a polymorphic clone, she demonstrates none of the tact or abilities that later clones would employ against the warriors such as phasing through walls and the like. Clone Yumi is barely capable of acting normal and notably refuses to speak to those unrelated to her objective, unlike her successors. Although this could be explained by X.A.N.A. not having perfected the polymorphic clones yet.
- Return to the Past is activated without anyone being at the Supercomputer to trigger it, having it instead just happen as soon as Aelita deactivates the tower.
- Evil Laugh: Fake Yumi has a pretty scary one.
- Green-Eyed Monster: In the final scene, Yumi jokingly pretends to flirt with Jeremie again when he says he supposedly knew the fake Yumi was a clone because of such behavior. Ulrich stops her and says how he's "had enough of that for one day". Yumi playfully asks him if he's jealous, giving him an Oh, Crap! reaction. Odd adds on how it sure looks like he's jealous as the others laugh about it.
- Hoist Hero over Head: The Fake Yumi does this to Jeremie.
- I Cannot Self-Terminate: Yumi cannot be devirtualized without Jeremie's input, from her own weapons, or without being killed by an enemy first, so the only way around this is for Ulrich to use friendly fire on Yumi.
- Inelegant Blubbering: As Yumi (the clone) flirts with Jeremie, the poor boy is reduced to this. This is the second episode in a row for this to happen to Jeremie (he reacts in the same way at Aelita's suggestion of trying out kissing when crossing over to Earth).
- Innocuously Important Episode: This is the first time XANA uses a type of minion that would later be called a polymorphic clone, a strategy he'd use many times in future episodes.
- The Jailer: Guardians are this for XANA, but are only able to hold one captive at a time.
- Mistaken for Cheating: Jeremie is mistaken for this when Ulrich and Odd walk in on him and the Yumi clone about to kiss.
- The Mole: Yumi's evil clone, though not a convincing one. Jeremie is the only one to remain skeptical, with everyone else assuming it was some form of a bad experience on Lyoko that's causing her to lash out.
- Nice Job Fixing It, Villain: X.A.N.A. proves that virtual dematerialization is possible (which is a little odd, as the previous episode ended with this knowledge), as well as giving Jeremie research into getting it to work again for Aelita.
- NOT!: Ulrich throws this on Sissi when she wants him to dump Yumi and go out with her.
- Oh, Crap!: Yolanda has one when the clone of Yumi roughly grabs her wrist in an effort to make her lay back down.
- Out-of-Character Alert: The gang knows that Yumi is acting off, but doesn't know why until near the end of the episode.
- Other Me Annoys Me: Yumi tells the duplicate that "You look like me when I'm having a bad day."
- Shower of Angst: Jeremie tries to invoke this on the clone of Yumi since he thinks Yumi is not herself. However, this does not work.
- What the Hell, Hero?:
- When Odd and Ulrich catch Yumi (actually a clone) and Jeremie about to kiss, Ulrich just glares at the two and leaves the room as Jeremie tries to tell him "It's not what you think", and Odd gives a sarcastic "Bravo!" They cool down later after Jeremie convinces them that something is off about Yumi.
- Earlier Jean-Pierre tears into Clone Yumi for getting violent with the nurse and attempts to punish her when she won't even talk to him... only to be cracked over the head with his telephone.
- Wounded Gazelle Gambit: Fake Yumi pretends to be swoon and sick when caught by Jeremie, simply to get him closer.
