It's almost the end of the semester at Kadic Academy. Aelita, Yumi, Ulrich, and Odd enter the lab to find Jeremie watching videos from Franz Hopper's diary that document his discovery of the Supercomputer's return to the past function, and how he relived June 6, 1994, over 2,546 times and became mentally unhinged. Jeremie then shows the rest of the group a specific video in which Hopper explains his plan to send himself and his daughter, Aelita, to Lyoko, where they will each hold a set of "keys to Lyoko" and live together forever. Jeremie deduces that these "keys" are what X.A.N.A. wants from Aelita, and Aelita herself concludes that, with them, X.A.N.A. would be able to escape from the Supercomputer.
Later, during breakfast in the school cafeteria, Jeremie reveals more news: X.A.N.A. did not give Aelita a virus, as was previously thought, but rather took something from her, a "fragment", which Jeremie has located inside Sector Five. Odd suggests they retrieve the fragment that night, after the End of the Year Dance, as their final mission. However, Aelita, who had been in a noticeably bad mood throughout the conversation, refuses to participate in the mission and storms out of the lunchroom. Jeremie follows her outside, and Aelita tells him about her new-found resentment toward her father, how she feels about the fact that he stole her childhood by bringing her to Lyoko, and that she never wants to go back to the virtual world ever again. Jeremie tries to reassure her that everything will be fine once they retrieve the fragment, but Aelita's bad mood persists saying that X.A.N.A. will never allow them to do that and even manages to steal her keys by force, and she walks off again.
Meanwhile, in the courtyard, many students try to find dates for the dance. Yumi attempts to ask Ulrich to be her date, but William distracts her with a proposal of his own, which she rejects. As Ulrich sees them talking, he assumes Yumi has agreed to go with William, and feels hurt and vindictive. So, when Sissi approaches Ulrich, he accepted her offer solely to get back at Yumi.
Unbeknownst to anyone, Aelita travels to the Factory, where she enters the Supercomputer room and shuts it down, causing her to lose consciousness and collapse. A short time later, Jeremie discovers the Supercomputer is unresponsive, prompting him to go to the Factory to fix the problem. When Yumi discovers Ulrich has agreed to go with Sissi out of spite, the two friends quarrel, leaving Yumi hurt and Ulrich ashamed of himself.
Jeremie arrives at the lab and finds the interface display blank. He then goes down to the Supercomputer room to check for problems, where he finds Aelita's body and the turned down Supercomputer. He hurriedly turns the Supercomputer back on, and Aelita regains consciousness. She explains she was willing to sacrifice herself to save the rest of the world, but Jeremie reassures her they can save it together and she can live a normal life afterwards.
That evening, Ulrich decides to stand Sissi up and instead goes to Yumi's house to apologize. Before he actually says anything, however, he is interrupted by a call from Jeremie, who asks him and Yumi to come to the Factory. Yumi accepts Ulrich's unspoken apology and the pair reconcile. Ulrich then calls Odd, who has failed to find a date due to his promiscuous reputation, and the three set off for the Factory together.
Odd, Ulrich, Yumi, and Aelita are virtualized onto the Ice Sector before Jeremie enters the Scipio code and the Transport Orb arrives to take them to Sector Five. In the Core Zone, a countdown starts and seven Creepers appear. Odd and Ulrich battle the Creepers while Yumi scales a large wall to reach the Key Mechanism. Once the Creepers are defeated, Yumi presses the mechanism, and the floor transforms into a downward-spiraling staircase, which the group descends.
At the bottom of the staircase, they find themselves beneath the core zone in a room with a long, narrow bridge, at the other end of which is Aelita's missing fragment. As they begin to run down the path, they are confronted by several Creepers. Odd, Yumi, and Ulrich stay behind to hold the monsters off while Aelita attempts to reach the fragment, but she is stopped when she finds a large gap in the bridge. Yumi and Ulrich rush to Aelita's aid while Odd stays behind to fend off the monsters. Odd is overwhelmed and devirtualized while Yumi and Ulrich work together to throw Aelita to the other side of the gap. Aelita makes it across, but Ulrich and Yumi are left dangling over the gap. The Creepers catch up to them and open fire. Yumi is devirtualized, but Ulrich manages to climb up and defend himself.
The bridge then begins to collapse, and Creepers, Ulrich and Aelita fall. However, Ulrich and Aelita's fall is broken by two Mantas, revealed to be under the control of Franz Hopper. The Mantas fly Aelita and Ulrich over to the platform with the fragment, and Aelita takes hold of it. It is then revealed that the fragment is a fake, a trap set by X.A.N.A., and the entire room begins to fall apart. Ulrich and the Mantas are crushed by falling debris, leaving terrified Aelita trapped on a platform in the center of the large room.
The Scyphozoa arrives and begins to drain Aelita's memory and everyone in the lab are forced to look at it. With no one to save her, the Scyphozoa succeeds. Aelita falls to the floor and slowly dies while the light starts to fade away from Sector Five and Lyoko itself begins to shut down. All across Lyoko, the towers turn red, and X.A.N.A., now possessing a set of Keys to Lyoko, finally escapes from the Supercomputer, much to the group's dismay.
Suddenly, a white light envelops Aelita's lifeless body, and she has multiple visions of her childhood on Earth, including her mother, her life in The Hermitage, visit in the lab for the first time and her virtualization, before regaining consciousness. The light returns to Sector Five, and Lyoko's towers turn from red to white. It is revealed by Jeremie that Franz Hopper has used his own Keys to Lyoko to restore the virtual world and that he has given Aelita back her missing fragment, which is discovered to be the memories of her past life. Jeremie manually devirtualizes Aelita, and he, Odd, Ulrich, and Yumi rush down to the Scanner Room to greet her, where she faints once again, this time into Jeremie's arms.
Later that night, all five Lyoko Warriors convene in Jeremie's dorm room. Aelita expresses a desire to find her father, who seems to have disappeared from Lyoko. They also discuss how Aelita is no longer tethered to Lyoko, but that X.A.N.A. no longer is, either, so shutting down the Supercomputer now will do nothing to stop him. Jeremie concludes that they must continue the fight, and he also promises to look for Franz Hopper. The rest of the group makes similar promises as they all hold hands with one another in solidarity.
- The original French name for this episode is Réminiscence.
- This episode originally aired as a double bill with Revelation.
- This is the only episode to feature the Lyoko Restoration Program.
- Franz Hopper is revealed to have relived June 6, 1994, over 2,546 times, which adds up to 6 years and 356 days.
- From this episode onward, neutral, deactivated towers as well as way towers glow white as opposed to blue and teal (for way towers). This is because Lyoko now runs using Franz Hopper's keys. Hopper used to turn towers white when he would activate them.
- It is revealed in this episode that Franz Hopper created X.A.N.A. to destroy "Project Carthage". It is unknown what that means or if this task was ever accomplished.
- This episode marks the first appearance of Aelita's mother, Anthea Schaeffer, which shows that Aelita's bright pink hair is inherited.
- Franz Hopper's possession of Mantas marks the only time in the series where someone other than X.A.N.A. controls a certain monster.
- In the flashback in which Aelita and her father are in the sewers, Aelita's voice briefly changes from a younger voice to her normal voice. It is unknown whether or not this is an error.
- Yumi's farewell clip in Echoes was taken from this episode.
- This episode got its own novel, but it was only released in French.
- The detail about Franz Hopper still being on Lyoko seems to have been forgotten by both Jeremie and Aelita during the first half of the episode, as neither of them seem to take it into account during their plans to shut down the Supercomputer.
|Code Lyoko: Season 2|
|New Order | Uncharted Territory | Exploration | A Great Day | Mister Pück | Saint Valentine's Day | Final Mix | Missing Link | The Chips Are Down | Marabounta | Common Interest | Temptation | A Bad Turn | Attack of the Zombies | Ultimatum | A Fine Mess | X.A.N.A.'s Kiss | Vertigo | Cold War | Déjà Vu | Tip-Top Shape | Is Anybody Out There? | Franz Hopper | Contact | Revelation | The Key|
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