Code Lyoko

A student named Milly seeks the comfort of her teddy bear after being embarrassed and ostracized due to her young age by Sissi, the school's bully/diva. Milly believes that her teddy is the only one that she can turn to for comfort and support. A corrupted super computer known as X.A.N.A. enters the real world by possessing the bear. In a quest to strike and destroy his enemies, the X.A.N.A infected teddy bear increases to an enormous size. No one is safe as this monstrosity creates a path of destruction.

Odd decides to start a music band with his friends. But Jeremy can't play, so they try to hire a drummer. In the end, the best drummer they can find is Nicholas (Sissi's blond-haired crony). As the group argues over whether or not to let Nicholas join the band (Ulrich and Yumi: Pro-Nicholas. Odd: Anti-Nicholas, Pro-Naomi), Jeremie alerts them that XANA is planning to overload a pylon and send this massive electric current through the telephone wires to blow up a nuclear power plant. Just in the nick of time, Aelita, Ulrich, and Odd stop XANA's plan. At the end of the episode, Odd gives in and allows Nicholas to be the drummer of his rock band.

Ulrich and Jeremy are doing graffiti on a wall on campus while Kiwi wakes up Jim. When Jim passes Ulrich and Jeremy, Ulrich gets away, but Jeremy just stays there and gets I'm trouble and has to stay in the campus over vacation. Sissy is being suspicious of Jeremy and thinks that he wanted to get in trouble. She asks her father to stay over the campus over her vacation, while she sorta spies on Jeremy. Jim is telling Jeremy to wash off the graffiti, then leaves while Jeremy gives Sissy the sponge and tells her (while mimicking Jim) to wash off the paint and later once again gets in trouble with Jeremy. Meanwhile, Xana has attacked again, this time spilling two toxic chemicals creating hazardous smoke. Sissy claims that she saw the smoke with arms and bumps into Jim who later finds the smoke after not believing in Jeremy and go into a small room where there is no vent and if they try to open the door, they can die. How will Yumi, Aelita, and Odd save the world and how will Ulrick find

Sissi has found something very special and dear to Ulrich, his diary! Unfortunately the diary contains some information on X.A.N.A. and Lyoko. Sissi decides to use this as a means of blackmail to get with Ulrich. Later Odd, Ulrich, Sissi, and some of the other students are going to a pool, the bus that their riding in is X.A.N.A.'s next target. He wants to ram the bus into a chemical plant. Now the team must head to Lyoko to help Aelita get to the tower to save the students and the rest of the city.

The day starts off when two girls are talking about Ulrich and then Sissi goes and interrupts and tells the girls that Ulrich is hiding his affections for her. Later, Odd, and Ulrich pull a prank on Sissi, giving her a txt message about a ""true love"". While the prank is being set, people in the town are experiencing difficulties due to a strange virus, now 2 trains are going on a collision course and one of the trains has highly toxic chemicals which can kill the town's population. Yumi cannot contact Ulrich and Odd because they shut off their mobiles. The prank is being set and Sissi opens a shed which happens to be Kiwi (Odd's dog)in there and jump om Sissy. Then Od gets in trouble after bringing Kiwi on the campus. Yumi finds the 2 and try to go to the factory, but Odd is stopped by Jim and is carried over to the principal. Now to help Aelida fix Xana, they will need everyone in the group, where is Odd when you need him?

Jeremie is working on the materialization program, and finally gets it. Jeremie wants to matierialize Aelita, but realizes that preparations need to be made. That night, Xana possesses two bulldozers and starts to destroy the factory. Odd and Yumi go into Lyoko where she falls into a virtual black hole. In order to save Yumi's life, Jeremie has to choose between either materializing her or Aelita.

After discovering Aelita's link to the supercomputer and the inability to shut off the supercomputer that stems from it, Jeremie works hard to find new and better ways to fight Xana. To that end, he develops new vehicles for the group. He also develops a new tower-scanning program that instantly detects activated towers, allowing Aelita to live on Earth. While adjusting to her new life, the class takes a trip to the nearby woods for a scientific field trip. Ulrich wants to partner up with Yumi, but she's already partnered up with someone named William.

While Aelita adjusts to her new life on Earth, Jeremie and the others investigate the mysterious owner of the Hermitage, Franz Hopper, and his link to the supercomputer, Lyoko, and Xana. It is discovered that Franz Hopper was in fact a former teacher at Kadic. After being teased by Sissi, Aelita retreats to Lyoko but gets lost. Jeremie finds her in a previously undiscovered fifth sector of Lyoko, The Carthage Region.

After discovering The Carthage Region, the group decides to explore it. Yumi is forced to opt out after her continued late-night trips to Lyoko draw the attention of her parents. While on The Carthage Region, Ulrich and Odd get dematerialized but don't appear in the real world, so Yumi sneaks out of the house to go to Lyoko and rescue Aelita from the Scyphozoa while Jeremie searches for a way to recover Odd and Ulrich. Unfortunately, Yumi's parents discover that she is missing and alert the school, who in turn discover that the other four are missing as well.

After taking another trip to The Carthage Region and returning to the school, Aelita talks to Jeremie about not being human, unaware that Sissi is recording their conversation. On top of that, the data they had retrieved from the Carthage Region takes over the supercomputer and starts running return trips over and over. Jeremie discovers that returning to the past makes X.A.N.A. much stronger and more powerful. During the third return trip, Xana possesses Sissi with his newly strengthened and increased abilities and powers and goes after Ulrich. Not only does the group have to deal with Sissi, but they also have to stop the return trips from continuing.

When Aelita's dreams and hallucinations become too disruptive to ignore, the group heads to the Hermitage to discover their source. There, Aelita finds a doll she inexplicably recognizes to be Mister Pück. Hidden on this doll is a key to a train station locker, which contains the heavily encrypted diary of Franz Hopper. Upon its discovery, Xana takes action, possessing Jeremie, to ensure they'll never be able to read it. When they deactivate the tower and Jeremie comes to his senses, Yumi explains to Jeremie why Xana can possess him and not Ulrich, Aelita, Odd, or Yumi.

It's Saint Valentine's Day and love is in the air. Ulrich forgets, so at last minute writes a poem for Yumi. However, when William presents Yumi with flowers, Ulrich gets jealous and reads the poem to Sissi instead, hoping to elicit jealousy from Yumi. The two end up in a fight, both bothered and wondering if the other really likes them. Also, a man possessed by Xana leaves a necklace at Aelita's door, Aelita is convinced that it was Jeremie who got it for her. Since Jeremie didn't actually get it, he's left to wonder who did, and ends up suspecting Odd, who avoids the question. This puts the two at odds, so to speak. Meanwhile, Aelita's necklace takes control of her and forces her to deliver herself to the Scyphozoa. Luckily, Odd arrives in time, and is able to save Aelita from the Scyphozoa by "threatening" to kill her.

After another three-week vacation, the group is still looking for a way to fight X.A.N.A.. X.A.N.A., meanwhile, is trying to destroy Lyoko, preventing them from doing just that. He does so by targeting the core, which contains the code that maintains the virtual world. In a side story, Odd blackmails Jim into asking Principal Delmas to make Odd have the same classes as his friends. Additionally, Yumi decides against having a relationship with Ulrich and decides it would be better if they were just friends. While defending the core, Aelita is suddenly devirtualized by the enemy. However, she still ends up back in the scanners and Jeremy realizes that this is because Aelita is fully human, just like the rest of the group, so she does not need Code: Earth anymore to be materialized on Earth.

During a field trip with the rest of her 10th grade class, Yumi finds herself facing off against the students, teachers, and bus driver, all of whom Xana has possessed. At the same time, Xana plans to get rid of Lyoko through an alternate means: destroying each sector one at a time. To this end, he uses the Scyphozoa to possess Aelita and enter Code:XANA into the way tower, wiping out The Forest Sector, realized by Jeremie.

Xana attacks the Lyoko warriors by possessing a large amount of food. At the same time, he bugs up The Mountain Sector by rising the digital sea, but Odd and Aelita go to Sector 5 to stop him. Xana also mounts an attack on Lyoko's core at the same time.

When Xana hacks into a weapon's manufacturing computer network and leaves a paper trail pointing to Jeremie, government agents arrive at the school looking for him. Then, the whole gang arrive at the factory. When they end up tracking Jeremie to the factory, Xana possesses them for an attack on the supercomputer itself in The Ice Sector, and in The Mountain Sector.

Aelita gets mad at Jeremie and she and Odd go into Lyoko without telling anybody, which causes problems. On lyoko, Xana creates a diversion to get everybody to deactivate the tower in The Mountain Sector while the monsters (mostly Mantas and Creepers) worked on destroying the core of Lyoko. Jeremie and Aelita find a strand of DNA that belongs to Franz Hopper, indicating he may be still alive.

Odd and Ulrich are talking in the shower room when a young boy, Johnny, asks to talk to Ulrich. It turns out that Johnny likes Yumi, and being jealous of that, Ulrich tells him to follow her around to get her attention, which Yumi hates. After following her all day and ending up in the gym, a flock of crows possessed by Xana attacks Yumi. She is beaten unconscious by their electrified beaks and sent to the hospital. Meanwhile, as Jeremie and the others are fighting monsters to deactivate the tower, the Scyphozoa possesses Aelita and has her enter Code:XANA into the way tower, wiping out The Desert Sector for good and leaving Lyoko with two main Sectors - The Mountain Sector and The Ice Sector. Once Jeremie finds out, he activates a return to the past with strong hope for Yumi's life. This episode proves that Ulrich is not as comfortable as being just friends with Yumi as he says he is.

Using the data that Franz Hopper gave them, Jeremie and Aelita succeed in recreating Lyoko, which now holds only Sector Five. Soon after, William is devirtualized, and seems perfectly normal. Sissi decides to make herself "editor-in-chief" of Kadic News, much to Milly and Tamiya's dismay. She soon barges into Aelita's room to interview her and is stopped by William. As soon as William makes Sissi, timay and milly leave,William kidnaps Aelita and takes her to Lyoko. William leads Aelita out of Sector Five and to what used to be The Desert Sector. His intent is revealed to throw Aelita into the Digital Sea. Odd manages to stop him, but William dives into the digital sea. Jeremie concludes that this is Xana's new strategy, and that they must be careful.

In order to compensate for all of William, while under XANA's control, Jeremie sets to work designing new equipment for his friends and recreating Lyoko. In order to buy himself time to do this, he activates a tower and uses it to create a a clone of his own to attend class in his place. Meanwhile, William's absence is drawing attention, from both the principal and his father. While Jeremie's Clone is impressing Jim outside, William appears on Lyoko and tries to put the tower under XANA's control. In order to maintain his clone, Jeremie draws energy from Sector Five to maintain the activated tower. He eventually runs out of energy and the tower is put under XANA's control. While Odd holds the Jeremie Clone off, Aelita, Yumi, and Ulrich go to Lyoko with new outfits and powers. They eventually deactivate the tower and stop William, who tries to push Yumi into the digital sea. She is saved by Odd at the last second. Jeremie then does a return to the past and replaces the Jeremie Clone with a William Clone to prevent any suspicion about his absence.

Jim's nephew, Chris, the drummer of the Subdigitals, pays a visit to Kadic to look for an opening act for the band's next concert. Everybody tries out, and Aelita turns out to be the one Chris is looking for. However, circumstances make sure that Chris does not realize who Aelita is, and X.A.N.A.'s clone of him only complicates matters, kidnapping Aelita and sending her to Lyoko. Jim and Chris manage to involve themselves in their search for Aelita, and end up battling the clone while the rest of the group tries to deactivate the tower. After the threat is over, Jeremy executes a return trip so that Jim and Chris remember nothing. He also delivers Aelita's demo CD to Chris personally after doing so.

There is a new recreation room at Kadic and William's clone is put in charge of it. Meanwhile, Jeremy has developed a program to get the real William out of Lyoko. However, the program malfunctions and bugs up the tower, allowing X.A.N.A. to take it over while Aelita cannot shut it down. As the William clone lashes out at the group, the real William is on Lyoko to keep the tower under X.A.N.A.'s control. Jeremy manages to repair the tower in time for Aelita to reset it, restoring the clone to working order. With a return trip to the past to erase the unwanted memories of William's behavior at school, the group elects Sissi as the rec room monitor.

The new virtual, submersible "submarine" (as Jeremy calls it) is almost complete, the last step being a secondary program that needs to be run by 4 PM the next day. However, when Aelita and Jeremy stay up late to set the program up, they are caught and given detention. Meanwhile, William takes the opportunity to attack the incomplete ship, forcing Yumi to run the Supercomputer in Jeremy's absence. Odd and Ulrich are unable to handle the situation, but Jeremy and Aelita are able to sneak out in time to help. Aelita is able to repel William with a massive attack, allowing Jeremy to complete the sub on time. It is later christened the Skidbladnir, nicknamed "the Skid" by Odd, after the Norse ship.

The gang manages to convince Jeremy to let them test out the Skid. During this test, the navigation system bugs up, leaving the gang stranded in the digital sea. Jeremy runs to his room to fetch the backup programs, but forgets that it's Fire Safety Day and runs into several teachers, eventually having to scale the roof to get to his room. Meanwhile, the Skid stumbles upon another Lyoko and is attacked by two eel-like monsters. Jeremy is able to repair the navigation system and bring his friends home, after which he surmises that the replica of Lyoko is created from the portion of the Keys to Lyoko that X.A.N.A. has stolen from Aelita's subconscious in the second season finale, The Key. Jeremy wonders how he plans to use it.