At the beginning of the story, Jeremie is working on Aelita's Materialization Program in the middle of the night. He almost completes it, but in the last moment, it doesn't work. He starts checking to make sure that Aelita connected all the data correctly, and in the process starts an argument with her. He apologizes for yelling at her, but she severes the link.
In the morning, Yumi comes to school to find Jeremie in a very bad mood. After telling her, Ulrich, and Odd about his argument, he decided to go to Lyoko himself and apologize. He gives Yumi the notes, which is a humongous collection. Once inside, Ulrich and Odd bow and step aside, after Odd says in a British voice "Your Scanner is waiting, sir." A problem occurs with the Virtualization process, and Jeremie is stuck in the Virtual Limbo, basically inside the wires connecting the Lab's interface computer with the Supercomputer below.
Yumi, who believes she is partially to blame for Jeremie's predicament, as she was controlling the Lab computer at the time, goes back to Kadic from The Factory to make sure the teachers don't get suspicious. Meanwhile, Ulrich is left in charge of the computer whilst Odd plays Tetris on his Game Boy.
Ulrich informs Aelita of Jeremie's problem, and, ever anxious about him, she agrees to help. According to Jeremie's theories, if she collects enough data from four Towers in the four known Sectors of Lyoko, Jeremie will be able to come back to the Scanners. She can communicate with Jeremie due to the fact their minds have melded inside the digital world.
X.A.N.A. sees the opportunity to trap one of the most important people in Team Lyoko forever in the Virtual Limbo. After Aelita recovers the data from the Desert Sector, Ice Sector, and Forest Sector, it finally realizes where Aelita needs to go next, and sends Bloks to guard all Mountain Towers. Ulrich wants to send Odd into Lyoko to help Aelita, but cannot control the Supercomputer well enough to do so. Yumi, due to her absence during most of the day, is taken to Mr. Delmas's office by Jim, who caught her trying to get out of the school.
Ulrich returns to Kadic to try and help Yumi, but cannot talk to Mr. Delmas directly, so he tries going to Sissi, who sees the chance to get rid of Yumi forever. Even after Ulrich promises to date her for a month, Sissi refuses to talk to her father to get Yumi out of trouble. Only after Ulrich gives her a "down payment" (a kiss on the lips) does she agree to get Yumi free of the teachers' wrath.
After she is out of trouble, Yumi virtualizes Ulrich to the Mountain Sector to help Aelita. Ulrich destroys the Bloks and Aelita is able to get all the Data back and is granted access to the Virtual Limbo. There, she wakes Jeremie up and touches his fingers, thus bringing him back to the Factory. There he is knocked out and found by the group, who take him to his room. When he wakes up, he claims that his experience was completly awesome. Jim is watching from below, rather confused (going "Hmm?" in a confused tone). Later, Ulrich calls Yumi on his cell phone, trying to explain the situation with Sissi, but she is really angry and hangs up.
- The original French name for this episode is Frontière.
- This is the first episode in which X.A.N.A does not attack Earth.
- This is also the first episode where a Return To The Past was not launched.
- This episode marks Jeremie's first (albeit failed) virtualization.
- In one scene Odd waits for Jeremie to come back from the virtual limbo, his stomach is shown like Yumi. Then his undershirt reappeared after Jeremie reappeared.