After studying Romeo and Juliet in class, Odd, Aelita, Ulrich, and Jeremie discuss the concept of dying for someone you love. Once Yumi arrives, the group notices a large crowd of students gathering in the courtyard, and discover Brynja Heringsdötir, Sissi's exceptionally beautiful pen pal from Iceland, has come to visit Kadic and has attracted the attention of male and female students alike.
With few exceptions, Brynja continues to captivate the student body for the rest of the day. After dinner, Odd accidentally bumps into Brynja on the way out of the cafeteria, and when she flirts with him, he becomes even more enchanted than before. In the rec room, Odd, Ulrich, and Jeremie begin to argue over Brynja, and Yumi and Aelita, two of the few students uninterested in the new girl, chide them all for being jealous before Brynja herself arrives to speak with Odd. After Odd leaves with her, Ulrich and Jeremie come to their senses, realizing the rift Brynja is causing in their friend group.
When Odd enters his dorm to prepare for a date with Brynja, he finds Ulrich, Yumi, Jeremie, and Aelita already there. Together, the four of them explain Brynja's disruption of their friend group, and how crucial their friendship is to fighting X.A.N.A. However, when the four ask Odd to stop seeing Brynja, Odd accuses them all of jealousy and storms out of the room. Later that evening, Jeremie and Aelita travel to the Factory and launch a program as they discuss Odd and Brynja. The two then leave the Factory to let the program run through the night.
Meanwhile, on their date, Brynja manipulates Odd into telling her about the Factory, and convinces him to bring her there. Having just missed Jeremie and Aelita, Odd and Brynja enter the Lab and find it empty. Brynja then begins tampering with the interface despite Odd's protests and unwittingly alters Jeremie and Aelita's program. Much later, in the middle of the night, Jeremie is alerted to an activated tower via the desktop in his dorm room, but the alert quickly stops itself, leaving him confused.
The next day, Jeremie and Aelita return to Factory to investigate the false alarm, and quickly discover that Brynja entered "parasitic foreign data" into the program the night before, causing widespread damage to the Supercomputer. Suddenly, the Superscan detects another activated tower in the Forest Sector. Unable to trust the Superscan because of Brynja's meddling, Jeremie reluctantly agrees to send Aelita to Lyoko to manually search for an activated tower while he notifies Ulrich and Yumi. However, the bug-ridden Supercomputer sends Aelita to the Ice Sector instead of the Forest Sector.
On campus, Ulrich and Yumi search for Odd after hearing from Jeremie, and find him with Brynja in the park. After a short argument, Yumi and Ulrich disown Odd from the friend group before heading to the Factory. Meanwhile, Aelita uses her Second Sight and detects no activated tower. However, when Jeremie attempts to manually devirtualize her, he finds this function is bugged as well, and Aelita ends up in Mountain Sector, where she is confronted by Bloks and Kankrelats.
As Jeremie works to repair the damage to the Supercomputer, Aelita battles the monsters. However, she is soon ambushed by William and is forced to flee. When Yumi and Ulrich arrive at the Factory, Jeremie attempts to send them to the Mountain Sector to help Aelita, but the bugged programs bring them to the Desert Sector instead, where they begin searching of a way tower. Aelita is eventually cornered by William and the monsters, and is captured by William's Super Smoke. However, Yumi and Ulrich arrive in time to save her, and a battle commences. Meanwhile, at the local swimming pool, Odd is wracked with guilt over his recent behavior, and decides to abandon Brynja and return to the Factory.
When Odd arrives at the Factory, he apologizes to Jeremie, who then agrees to send him to Lyoko to help the others. Meanwhile, in the Mountain Sector, Ulrich and Yumi are each devirtualized by William and a Blok, respectively, as Jeremie succeeds in fixing the Supercomputer. As William closes in on Aelita, Odd arrives in the Mountain Sector and defeats William. However, in a last-ditch effort, William shoves Aelita off a cliff as he is devirtualized, and Odd jumps off after her. With a well-aimed Laser Arrow, Odd triggers Aelita's star bracelet, causing her Angel Wings to open and saving her from the Digital Sea. Aelita then catches Odd and carries them both back to safety.
In the Scanner Room, Odd apologizes to the others, who accept his apology and decide to keep him in the group. Jeremie decides against performing a Time Reversion, convinced Brynja is not nearly as interested in revealing their secret as she is in manipulating people. The next day, Brynja leaves early to see the French countryside at Sissi's cousin's house, and the Lyoko Warriors celebrate her departure. Sissi, who felt overshadowed by Brynja during her stay, is revealed to be relieved as well.
- The original French name for this episode is La belle de Kadic, which translates to The Beauty of Kadic.
- When Odd enters his dorm room and finds his friends have gathered inside, he breaks the fourth wall by confusedly asking "Did I miss an episode?"
- In this episode, William is noticeably more talkative than usual. It is unknown why this is.
- This is the only episode in which Brynja Heringsdötir appears.