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Missing Link is the eighth episode of Season 2 and the thirty-fourth episode of Code Lyoko.


At the Factory, the gang is waiting for Yumi who is running late for a treasure hunting mission to Sector Five. In the scanner room, Ulrich wonders what could be keeping her and Odd makes a teasing remark that she might be spending time with William. This results in a jealous "Hmm?" from Ulrich, to which Odd responds with "I said maybe." Jeremy responds to Aelita that his research on the anti-virus is going very slowly due to a lack of some very important codes, but the Lyoko Warriors are holding out hope that this retrieval mission to Sector Five will yield promising results. At this time, Yumi is seen hurrying through the sewer passage to the Factory. She arrives at the factory just after Jeremie sends the others to Lyoko and tells them to wait for her while he sends her to meet them. 

When she lands in the Forest Sector, Ulrich asks Yumi where she was. When she gives him a vague answer, saying she "had something to do," he impulsively accuses her of being with William. She responds by asking if he ever gets tired of being jealous and saying it is none of his business. They clash, Yumi telling Ulrich to believe whatever he wants and to be a jerk if he wants to and Ulrich responds, "You must think I'm really dumb."

Several Kankrelats then arrive and they battle with the creatures, winning easily. While the Kankrelats occupy Odd and Ulrich, the Scyphozoa arrives on the scene undetected and sets its sights on Yumi this time instead of Aelita. When suddenly alerted to the monster's presence by Jeremie, the scyphozoa already has Yumi in its grip, syphoning away her data before Ulrich comes to the rescue. With the scyphozoa's attack thwarted, the monsters flee and Yumi is left not feeling quite right. Confused as to why X.A.N.A. had the Scyphozoa attack and go after Yumi instead of Aelita, its main target, Jeremie decides to abort the mission and activates the devirtualization program to figure this out.

He starts with Yumi, Odd, and Aelita, but only manages to retrieve Odd and Aelita. Worried, he assures Yumi that he must have hit a wrong button and tries to bring Yumi back with Ulrich this time. Ulrich comes back just fine, but everyone is shocked to see Yumi still has not returned. Distraught, Jeremy informs Yumi that he can't rematerialize her, so he tells her to hide in an inactive tower while he attempts to figure out the problem.

Jeremy tells Yumi that he'll have this problem figured out in due time, but Yumi tells Jeremy that XANA is the least of her concerns: Picture Day for the ninth graders is this morning and anyone from Yumi's class who fails to show up without a solid excuse will face one day suspension (not something she'll ever be able to smooth over to her parents). Odd proposes that he'll go in disguise and take Yumi's place in the picture. Ulrich actually agrees to the idea as long as it's not Odd posing as Yumi. Instead, he has somebody else in mind. At the school, Ulrich asks Sissi, fresh from the showers, to pose as Yumi and that he'll do "almost" anything in return.

At the Factory, Jeremie hypothesizes that when the scyphozoa attacked Yumi, he infected her with some sort of virus. However, Yumi wonders if it took some of her memory, which Aelita says is unlikely since it's her memory XANA wants, not Yumi's. Jeremy finally concludes that if it wasn't her memory, then the scyphozoa must've taken something else and runs a scan of Yumi to get to the root of the problem. To his horror, Jeremy discovers the urgency of the situation by telling Yumi exactly what the problem is: The scyphozoa stole Yumi's computerized code sequence for her human DNA. Jeremy explains that this is the most vital code her virtual manifestation contains because it defines her molecular structure, which is what the supercomputer uses from memory to transport a person in or out of the digital realm. Without it, the supercomputer cannot return Yumi to her physical form in the scanners and thereby has no way of ever getting back to Earth.

At the school, Ulrich explains Yumi's absence and requests Sissi to stand in for her in the photo. Shockingly, she agrees without demanding in return for once.

Yumi is devastated to know that she is permanently stranded on Lyoko and urgently demands for Jeremy to find a solution. Jeremy vows to do everything he can bring her home. Just then, Aelita is struck with an idea and has Jeremie send her back to Lyoko, though she refuses to reveal her plan to him.

15 minutes later, Sissi comes out wearing a wig that makes her look exactly like Yumi's, but with a dress that doesn't match Yumi's fashion style at all. Ulrich then decides to go get one of Yumi's own dresses for Sissi to wear. The boys are still perplexed at how cooperative Sissi is being. As Aelita is virtualized, Ulrich arrives at the Ishiyama house and sneaks in through the side door, ordering Odd to keep a lookout. Meanwhile, Aelita makes her way to the tower Yumi is hiding in on the overboard. While Ulrich sneaks through Yumi's house undetected (Yumi's parents, Takeho and Akiko, can be heard arguing in the background), Aelita closes in on the tower, still refusing to tell Jeremy what she's planning. She reaches the tower just as Ulrich reaches Yumi's bedroom and finds the dress. Aelita finally reveals her idea: She's going to activate a process that will transfer her own DNA sequence code to Yumi's virtual structure, sacrificing her place on Earth to Yumi. Jeremie tries to protest to this, but Aelita insists Yumi's place is on Earth and that if anyone should remain on Lyoko, it should be her. Before Jeremy can tell her to stop, she cuts off the signal with him and they begin the transfer. Jeremie's analysis of the process then reveals how dire this situation is, as well as XANA's master plan.

Back at Yumi's house, Ulrich secures the dress and prepares to make his escape when Akiko shows up to awaken Yumi for school. His phone rings, but some quick thinking by Ulrich has her believing that Yumi just forgot her cell phone when she left to school. Once she leaves, Ulrich climbs out of the window and meets up with Odd, who has been playing a racing game on his Game Boy instead of standing guard. Now in the clear, Ulrich is able to take Jeremy's call and he explains what Aelita is up to. Jeremy elaborates that if the DNA transfer process is allowed to be completed, X.A.N.A. will be given free access to take Aelita's memories at will, revealing that the scyphozoa's attack on Yumi was an extremely well-planned ruse from the very beginning to use her as bait that she is just minutes away from falling to hook line and sinker. Since Aelita knew Jeremy wouldn't approve, Jeremy is unable to warn her of these consequences because she's severed all contact with the tower. The only way to thwart this evil scheme is if Odd and Ulrich hightail back to Lyoko before it's too late. So, they head back to school, give the dress to Sissi (who accepts her own mission), and head to the Factory with only ten minutes on the clock. The boys make it to the scanners just as Sissi arrives at the photoshoot and they are off to Lyoko. At the class picture, Sissi tries to blend in with the crowd while posing as Yumi. William almost immediately notices that she isn't Yumi, which catches the attention of the rest of the class, notably Mathias.

On Lyoko, Aelita has nearly finished transferring her DNA sequence over to Yumi. With help from their vehicles, Odd and Ulrich arrive at the tower in just the nick of time to stop Aelita's transfer. She apologizes and tells them she wanted to do the right thing, but Yumi reassures her that she appreciates what she wanted to do for her. Odd even remarks that confusing generosity with stupidity is the mark of a true human being. With XANA's evil scheme thwarted, the warriors still have to figure out how to help Yumi. Jeremie has another ingenios idea; since X.A.N.A. stole Yumi's DNA code sequence, it must be locked away in its own memory, which means there's only one place it could be: Sector 5.

At the photoshoot, the photographer is readying his camera and hostility starts escalating gradually since everyone can't help but wonder shy Sissi is dressed up like Yumi. All of the commotion and Sissi telling the classmates to be quiet alerts the principal, who instantly notices his daughter once he comes to the scene. Sissi says that she has a good reason for what she's doing just as the photographer captures the scene.

The gang arrives in the Sector 5 Arena. Before the warriors go through with the mission, Jeremy warns Yumi that without her DNA code sequence, she's just as vulnerable as Aelita; she can't be devirtualized or she'll be gone for good. They charge forward when the hallway opens up and have three minutes to escape the core zone when the countdown commences. Jeremy informs the group the switch can be seen at the end of a corridor across a room. They reach the chamber (a huge room with only a narrow bridge for a floor dividing the chasm beneath them) and suspects it's a trap, but Odd takes off anyway to get to the key. It turns out that the ceiling is booby-trapped with crushers and unsuccessfully attempts to crush Odd as he runs along the platform, being saved by Ulrich. With only one minute remaining to turn the key, they manage to make it halfway across, but a misstep by Ulrich forces Odd to sacrifice himself, being crushed alive and devirtualized. Ulrich soon reaches the switch and shuts off the timer. Once the door opens, they all take the elevator to the celestial dome where the access panel is.  

While Aelita searches for the DNA sequence, Ulrich apologizes to Yumi for their earlier argument and admits that it was none of his business what she had been doing. While Yumi agrees, she tells him she was buying two tickets to the Subsonics concert but was having a hard time due to a bad internet connection. When the Flying Mantas hatch, they attack hard as Aelita manages to find the DNA sequence and quickly sends it to Jeremie. Just as Jeremy downloads the missing link back into Yumi's virtual envelope, she begins to tell Ulrich how happy she is to go back home. However, she is suddenly struck down by a Manta and Ulrich, unsure if Yumi might be gone for good, angrily kills the Manta as Aelita asks Jeremie if he restored Yumi's DNA sequence in time for her to be saved. Jeremie tells them to hope for the best and Aelita and Ulrich head back out of the sector on the overbike.

In the scanner room, Yumi has been returned to Earth safe and sound, just out cold on the floor, as Ulrich rushes over to her and holds her in his arms. Yumi wakes up and looks up at Ulrich, who smiles at her and she smiles back at him. Odd recovers from the mission as well, stating that getting devirtualized in Sector 5 feels like being flattened by a steamroller.

Back at the school, Sissi has taken the heat for Yumi's absence, but assures them she got Yumi out of punishment as she took the blame and returns Yumi her dress. As a gesture of gratitude, Yumi gives Sissi one of the tickets she bought so she can go with Ulrich. Odd is still suspicious of Sissi's selflessness and Aelita theorizes that Sissi might actually be a good person deep down, but Jeremie bluntly says "or she's just crazy about Ulrich." Odd ends the episode by simply stating "What a mess!"


  • The original French name for this episode is Chaînon manquant.
  • This was the first episode where the Scyphozoa attacked someone other than Aelita.
  • This was the only time X.A.N.A. tried to steal Aelita's memory without using the Scyphozoa to attack her.
  • This was the second time Yumi was at risk of disappearing forever if she ran out of life points.
  • This is the second time X.A.N.A. victimized Yumi and made her the bait for one of it's evil schemes, the first being Image Problem, where it abducts her and replaces her with an evil clone.
  • This was the third time Ulrich asked Sissi for a favor and the first time she did so willingly.
  • This episode shows that Aelita can transfer her DNA codes to someone who does not own any on Lyoko.
    • Replacing Yumi's lost DNA with her own could result in unintended consequences, such as causing her friend to become Caucasian.
  • The room with the booby-trapped ceiling in Sector Five would later reappear in Nobody in Particular.
  • Easter Egg: When Ulrich arrives in Yumi's bedroom, he sees a stuffed plushie of Totoro from the Studio Ghibli film, My Neighbor Totoro.


  • At the beginning of the episode, Jeremie uses the normal materialization program to devirtualize Aelita, which should not have worked since, at this point in the series, she still requires the Code: Earth program to return to Earth.
  • When the photographer tries to take the ninth grade photo, his camera was shown upside down, but when he took the photo, it was right side up again.
  • When Odd and Ulrich are running through the room in Sector Five, Jeremie tells them that they only have one minute left to trip the key when the Factory Interface shows that they still have a good two minutes.