A call late at night wakes up Yumi. She answers and Jeremie responds, saying that XANA has activated five towers. He tells her to get to the Factory immediately. She meets up with the others in front of the elevator at the Factory. When they arrive at the Lab, everyone is surprised to see a man typing on Jeremie's computer. The man turns around, revealing him to be an older man with glasses and a thick beard. To Jeremie's surprise, this enigma deactivates all five activated towers from the computer. This only puzzles everyone more, and finally, the man identifies himself as Franz Hopper, the man who created the supercomputer. He explains that he lost control of XANA, who was built to counter a military project based on a multi-agent system. He also says that he created Aelita to be Lyoko's guardian, but he never expected to see her in flesh and blood. Skeptical, Ulrich asks where he has been for the last ten years. Franz Hopper responds,"Well, let's say I was a kind of...prisoner, who finally managed to escape." He promises he will find Aelita's antivirus and shut down the supercomputer. Unbeknownst to the heroes, this character is actually XANA-Franz Hopper, the newest Polymorph sent by XANA.
Later on that night, Aelita tells Jeremie,"He's very fatherly...Actually, in a way, he is my father." The next morning, Jeremie is awoken by a cell phone call from his father, Michael. His friends sneak into the room and shout "happy birthday!" to him. As they crowd around Jeremie, his father asks if he's thought about going to a school for gifted children. Hurriedly, Jeremie says "yes" and hangs up. Odd hands Jeremie a present, which is revealed to be a drawing of them all, symbolizing their friendship. In the middle of the festive mood, Jeremie suggests they go to the Factory and check up on Franz Hopper. When they get there, Franz balks at the idea of virtualizing people, saying it's a dangerous procedure with deadly side-effects such as cell degradation. They decide to check for such a problem. Odd, Ulrich and Yumi enter the Scanners to get checked. Odd and Ulrich seem fine, but Yumi's scan shows she is suffering from cell degradation in her mind. Yumi leaves to do some thinking. Odd and Ulrich find this unforgivable and blame Jeremie for not telling them the danger of virtualization.
At dinner that night, they continue to blame him for Yumi's "imminent" death, saying he's supposed to be the smart one and the team leader. Disgusted, Jeremie pulls out of his seat and walks away. Aelita scolds Ulrich, telling him that the Scanners were responsible for her being on Earth, and leaves with Jeremie. At the Ishiyama house, Yumi is uncomfortably silent at the dinner table. Even Hiroki's annoying comments aren't being responded to. She says she's not hungry and goes to her room. None of Yumi's friends could sleep that night, knowing her "fate". As Yumi stares into nothingness, her cell phone rings. She picks up and hears XANA-Franz Hopper, who says he has good news and to tell the others to go to the Factory in the morning after they have gotten some sleep.
The next day, the Lab doors slide open and Team Lyoko enters. XANA-Franz Hopper tells them that he knows how to program the antivirus for Aelita. All he needs is data from Carthage. Jeremie asks why they should go, considering his comments on the dangers of the Scanners. Exasperated, Jeremie asks what he's supposed to do. The Spectre coolly responds, telling him to stay out of the way. Jeremie vents his growing frustration, complaining that everyone blames him for everything. XANA-Franz Hopper turns around and retorts, "But you were the one who played the sorceror's apprentice. You're the one who put your friends' lives at risk, and you're the one who let XANA destroy my diary!" Tired of the hostile atmosphere, Jeremie leaves and goes back to Kadic. The other three are more than happy to go on their "final" mission to Lyoko. In his dorm room, Jeremie stares at the group picture Odd drew for his birthday. He sadly puts it down and calls his father, saying he wants to go to the school for gifted children. His father says he'll be there tomorrow to pick him up. In the Lab, XANA-Franz Hopper virtualizes Odd, Yumi, and Ulrich directly into Carthage's Arena, much to Odd's surprise at not getting sick. Meanwhile, Jeremie continues to contemplate XANA-Franz Hopper's statement: "You're the one who let XANA destroy my diary!" He realizes that the real Franz couldn't have known about the destroyed CDs; only XANA does. He then starts running back to the Factory to warn his friends that the man in the Lab is actually one of XANA's servants. On Carthage, Odd, Ulrich, and Yumi reach the Core Zone, where they are confronted by many Creepers. XANA-Franz Hopper assures them that he programmed new weapons. The three don't see an improvement in their weapons, but when the fire them, performance is much better. Odd's laser arrows track down targets and destroy multiple Creepers; the same effect is applied to Yumi's tessen fans. Ulrich charges up his katana and swings it, releasing an energy wave that destroys two Creepers. He then touches the Key, stopping the three-minute countdown. Odd is begging to cut down more monsters, clearly enjoying the rage and thrill of battle. The fake Franz assures him that he has plenty more "surprises" for them.
XANA-Franz Hopper asks Aelita, who is in the Scanner Room, if she's ready to go to Lyoko. The Scanner doors open up, but she's stopped by Jeremie, who tells her to keep quiet, knowing that the Polymorphic has been scamming them. Aelita appears in the Desert sector, alone. She is trapped on a small island above the abyss. Jeremie comes into the Lab and declares that he is XANA. Immediately, the Eye of XANA flickers in the man's glasses, confirming his suspicions. He electrocutes Jeremie, knocking him aside. In Carthage, Team Lyoko's weapons stop working as a group of Creepers block them off. They jump off the path, onto another one, parallel to the original. They realize that they have been double-crossed. In the Lab, XANA-Franz Hopper has made a few modifications, ensuring that they will not return to Earth if they are devirtualized, but either killed or trapped in Lyoko forever. In the Desert sector, the Scyphozoa arrives to take Aelita's memory. On Carthage, the three run into an activated tower that is separated from them by a chasm. The Creepers come up behind them and start firing. Out of options, they begin to engage the Creepers in hand-to-hand combat. Odd even turns the fight into a little boxing match, jabbing at the Creeper left and right. Meanwhile, the Scyphozoa drains Aelita's memory and energy in the Desert.
The Scyphozoa seems to have drained all of Aelita's memory, but something is wrong. Unfortunately for XANA, the Aelita on Lyoko was actually a decoy. The real Aelita was in the Scanner Room the whole time, controlling the decoy using Jeremie's laptop. Angry for being tricked by Jeremie and frustrated by failing his mission, XANA-Franz Hopper reverts back into a specter and goes up into the ceiling, returning to its master's. In Carthage, the Lyokons are cornered. Ulrich loses all his life points, but Jeremie has taken control again. He brings Ulrich back and returns the weapons of the other two, allowing them to take out the Creepers. As this goes on, a Manta flies in. Aelita virtualizes into the Ice Barrier Sector, where the Transport Orb takes her to Carthage. In the Lab, XANA-Franz Hopper returns, entering Jeremie's body and blocking his airways, so that he slowly suffocates. Ulrich comes up from the Scanner Room and sees Jeremie suffocating, but there's nothing he can do about it. Aelita runs into the room with the activated tower. She uses the Manta as a stepping stone and leaps across the chasm, landing inside the tower. Immediately after she deactivates the tower, XANA-Franz Hopper dies, leaving Jeremie's body, allowing him to breathe again. Later in the day, Jeremie tells Yumi that he checked and found nothing wrong with her, biologically. A knock on the door directs everyone's attention to Jeremie's father, who asks him if he's ready to leave. He goes out into the hallway to get away from his friends. He then tells his father that he's changed his mind, and doesn't want to go anymore. His father takes it well and tells him it's okay. When he comes back into his room, his friends ask where he was planning on going. Jeremie tells them "nowhere". He walks over to his desk and can't help but show Odd's picture again.
This episode contains examples of:
- Birthday Episode: It's Jeremie's birthday, but only for a third of the episode. He enjoys it until he gets to the factory.
- Batman Gambit: XANA disguises himself as Franz Hopper and manipulates the heroes into turning against Jeremie, by lying to them with false information.
- Callback: To Mister Puck, where Jeremie works out that the Franz with them is a fake, as he couldn't possibly know about XANA trashing his diary.
- Deconstructed Trope: This episode reminds us that for all of their adventures, the Lyoko Warriors are children dealing with highly advanced technology of dubious origin. XANA!Franz leveraging this angle to make it seem that they were putting their lives at risk because of potentially unsafe technology, in one fell swoop, seems to completely destroy the whole Wake Up, Go to School & Save the World premise of the series and pretty much leaves the group in tatters. It's enough that even if it was just a lie made up by XANA, Jeremie takes the idea seriously enough to recheck the system and its workings after the attack is foiled, thankfully confirming that the scanners are, indeed, safe for use.
- Equipment Upgrade: Courtesy of XANA!Franz Hopper, though it only serves to gain their trust before he deletes their weapons altogether.
- Flashback-Montage Realization: To Mister Puck, where Jeremie works out that Franz couldn't possibly know about XANA trashing his diary.
- Freeze-Frame Bonus: In the cafeteria, Sissi can be seen for a few seconds in the table next to the heroes', apparently listening in on their conversation.
- Manipulative Bastard: XANA tried jealousy to separate the group, this time he tries discrediting Jeremie and pushing him out of the group by making it appear as though he recklessly endangered their lives, a far more powerful and legitimate lever. Jeremie gets so depressed, he even calls his father to transfer him to a gifted kids school.
- The Mole: XANA!Franz is not the real Franz Hopper, and makes efforts to efficiently make them distrust Jeremie. He particularly influences Yumi, making her believe that Jeremie had given her an illness related to using the supposedly-unsafe scanners.
- Mood Whiplash: This episode starts off with its usual drama, then it switches to a lighthearted scene with Jeremie's friends celebrating his birthday. It goes downhill from there.
- Near-Villain Victory: XANA almost succeeds, had it not been for some quick-thinking by Jeremie to use a clone running from his laptop in place of Aelita, not to mention piecing together the Signature Item Clue that only XANA and the gang knows about his diary being destroyed.
- Out-Gambitted: XANA had the perfect plan to separate the Lyoko Warriors to destroy the main three and steal Aelita's memories in one fell swoop. Unfortunately for him, Jeremie figured it out thanks to his Franz specter Saying Too Much and blind-sided him with an Aelita decoy.
- Saying Too Much: The only people with knowledge of the diary entries are the Lyoko Warriors and XANA, not Franz Hopper. The quote "And you're the one who let XANA destroy my diary!" from XANA!Franz gives this away to Jeremie.
- Sinister Suffocation: This episode is one of the few episodes in which the villain displays genuine fury towards the heroes. After falling for Jérémie's trap, X.A.N.A.'s spectre suffers a Villainous Breakdown that causes its body to degenerate into an amorphous smoke cloud. Rather than try to reassemble its physical body like in previous episodes, the spectre impulsively invades Jérémie's body and clogs his airways, in a desperate and maddened attempt to kill the boy.
- Supernatural Suffocation: XANA cannot take control of Jeremie, but can suffocate him as retribution for messing with his plans again.
- What the Hell, Hero?: XANA!Franz Hopper does this to Jeremie to make him leave the group. Also doubles as a "The Reason You Suck" Speech:XANA!Franz: Perhaps, but you're the one who played the sorcerer's apprentice; you're the one who put your friends' lives at risk; and you're the one who let XANA destroy my diary!
