- This article is for the episode. For the character, see Aelita Schaeffer.
Aelita is haunted by traumatic memories of losing her father to X.A.N.A. and begins having disruptive daydreams. At lunch, Aelita becomes angry when Jeremie shows a lack of sensitivity toward the subject of her past, and goes to The Hermitage to sulk. Odd finds her and apologizes on Jeremie's behalf, adding that Jeremie "really likes" her. Aelita then convinces Odd to come with her on a secret trip to Lyoko in order to search for signs of Franz Hopper.
Meanwhile, Jeremie and Ulrich are alerted to an activated tower in the Mountain Sector while studying in the campus library. They call Yumi, and the three of them arrive at the Factory. Jeremie finds he cannot get in touch with either Aelita or Odd, completely unaware that they are already on Lyoko and have entered Carthage.
Ulrich and Yumi are sent to the Mountain Sector, and are immediately attack by Tarantulas and Hornets. In Carthage, Odd and Aelita reach the Core Zone and defeat several Creepers before touching the key and entering the Celestial Dome. Jeremie finally discovers Aelita and Odd in Sector Five, and demands they go to the Mountain Sector. However, several Monsters are discovered near the Core of Lyoko, and Jeremie realizes the activated tower is simply a diversion meant to occupy the Lyoko Warriors while X.A.N.A. destroys the Core.
Ulrich and Yumi, who have been battling Bloks, abandon their defense of the activated tower and are sent to Sector Five. Meanwhile, Aelita and Odd fend off swarms of Mantas in the Celestial Dome, and Odd is devirtualized. Aelita enters the room containing the Core, followed shortly after by Ulrich and Yumi, and together they defeat all the monsters. Jeremie suggests Aelita stop at an interface to collect data on Franz Hopper before deactivating the tower, indicating he has learned to be more sensitive to her feelings, and Aelita happily complies.
Later that night, Jeremie and Aelita use Jeremie's dorm room desktop to analyze the data she collected. Jeremie discovers a fragment of Franz Hopper's DNA, which they take as evidence that he may still be alive.
- The original French name for this episode is the same as the English.
- This is one of two episodes named after a character, the other episode being Franz Hopper.
- Odd's foot odor, a major subplot in this episode, is a running gag throughout the series.
- At the beginning of the episode, Mr. Fumet teaches a lesson on Ragnarök, a tale in Norse mythology in which a natural disaster destroys the world. A new world then arises and is repopulated by a single man and woman. This foreshadows the third season finale, in which X.A.N.A. succeeds in destroying Lyoko, only for it to be rebuilt by Jeremie and Aelita.
- This episode got its own novel, but it was only released in French.