Ulrich is alone in the Scanner Room, flipping an Euro to see who comes out of the Scanners first. He seems to have lost the bet with himself as Yumi comes out first, but immediately afterwards, Odd comes out with Yumi's voice. Yumi speaks with Odd's voice. In the Lab, Jeremie discovers a bug in the materialization program caused Odd and Yumi to switch bodies. He tells them that he may have a solution to this mess by tomorrow morning. Odd complains that his back itches and says it's the straps of Yumi's bra. Yumi orders him NOT to take it off.
The two are uneasy at the prospect of spending the night in each other's life. When they climb out of the sewers into the Park, they ask each other their plans for the day. Yumi tells Odd to act Japanese, not act stupid, eat with chopsticks, and go to bed early. Ulrich asks Odd about his plans for the day. Odd recalls that he's supposed to break up with Magali De Vasseur and Claire Girard. Later in the day, Ulrich and Odd, who is in Yumi's body, tells Ulrich to practice asking out Yumi on him. Ulrich rejects that action as Sissi comes by. She calls Yumi, whose body Odd inhabits, a stringbean. Odd comes back with a comment on her mental capacity and puts his head on Ulrich's shoulder. Disgusted, Sissi walks away as Tamiya Diop snaps a picture of the two together for the school newspaper. Ulrich threatens Odd with death if he does that again and leaves.
In Odd's room, Yumi fingers through a drawer to get a green handheld device. As she gets it, Kiwi growls at her, knowing that Yumi isn't his master. Yumi gets the object and leaves. In the hallway, Yumi is confronted by Magali De Vasseur. Magali slaps Yumi across her left cheek, saying she knows about Claire. Moments later, Claire Girard comes by and slaps Yumi across her other cheek, saying she knows about Magali. Sissi comes and tells her Ulrich will need a new date once his stringbean drops. When she leaves, Ulrich comes in, asking if she got "it". Yumi asks him what Sissi meant by "stringbean". Ulrich tells her it's nothing. As the two walk out of the Dormitory, Milly Solovieff and Tamiya Diop grill Ulrich with questions for the newspaper's gossip section. Ulrich refuses to answer as they walk past.
When Yumi asks what's going on, Ulrich tells her to ask "that imbecile, Odd". When they reach the cafeteria, Odd asks, "Well, did you find it? I've had it since I was really little." That night, Mr. Ishiyama asks his daughter why she isn't eating. A piece of sushi slips out of Odd's chopsticks, much to his embarrassment. Then, he has a flashback in which Yumi hands him the green device, telling him it's only for an emergency. Odd puts down his chopsticks and pulls out the green device. He pulls off the top, revealing the device a large fork for small children. He jams it into a piece of sushi and puts it into his mouth. As he looks around him, seeing Yumi's family staring in disbelief at him, he tells them that he's going to bed and leaves the dinner table. Hiroki declares his big sister's actions as an effect of love. In the bathroom, Odd sees his hands flicker and momentarily become partially transparent, something that obviously shouldn't be happening.
At Kadic, Yumi notices the same effect while stroking Kiwi. Ulrich comes into the dorm room and tells Yumi to be careful as she removes her shoes. When she takes them off, she is overwhelmed by the stench. The next morning, Jeremie, who has been working all night, confirms the problem as a bug in the materialization program. In Ulrich and Odd's dorm room, Yumi wakes up and sees her hands transparent for a moment. At the Ishiyama house, Odd stares at his hands and arms as they flicker. Later in the day, Yumi describes the symptoms to Jeremie. Jeremie says that all they need to do is restart the materialization program from Lyoko. Yumi stops in disbelief when she sees what Odd has done with her body. Odd in orange and lime green clothes contrast sharply against Yumi's normal black clothes. As Yumi yells at Odd, Tamiya stops by again and takes a picture of Yumi's clothes. Milly tells them that these rather scathing pictures will double circulation. Yumi asks Odd again what they mean by love. Odd leaves without answering her question.
In Mrs. Meyer's class, Odd is asked by William if she always talks to herself. Odd tells him it's because of a split personality. Faced with a pop quiz on linear functions, Odd asks if he/she can go to the Infirmary. Mrs. Meyer lets him go. He meets up with the others. Jeremie explains that because they aren't in their original bodies, they are unstable. He also says that if they don't deal with it soon, they will disintegrate.
At the Factory, Jeremie virtualizes them into Lyoko. Yumi and Odd, still not in their original bodies, struggle to move in the Ice Sector. As Aelita enters a tower to restart the program, Odd and Yumi's bodies begin to disappear. It's only temporary, but it's markedly worse than before. Faced with a group of Roachsters, they struggle to use each other's weapons. In the tower, Aelita discovers she can't reboot the materialization program from the tower. After Ulrich destroys the Roachsters, Aelita comes out saying they have to get to Sector 5. They take their vehicles to get to the edge of the sector. As the Transport Orb is summoned, Ulrich is devirtualized by a Megatank. The Transport Orb then takes the other three to Carthage.
When they get there, Yumi comments that she feels sick, something normally associated with Odd. They run into the Arena and follow an elevated walkway. Unknown to them, they are being followed by Creepers. They reach a dead-end with the Key situated above an abyss. They see no way of getting to it. A Creeper causes Odd to fall off the edge, but he doesn't fall because XANA has modified gravity. Instead, he floats and begins to swim towards the Key. Unfortunately, he doesn't have enough momentum to reach it. Yumi asks how many life points he has left and Odd tells her plenty. Yumi fires a Laser Arrow at Odd, pushing him enough for him to touch the Key. A door opens up on the side of the room opposite Aelita and Yumi. Odd pushes off, getting to the other side. Aelita and Yumi jump across the abyss, but a Creeper fires at Yumi, pushing her to the other side, but leaving Aelita stuck in the middle. The Scyphozoa arrives to take her memories, but a well-placed Tessen Fan by Odd severs its tentacles. Odd jumps back out and Yumi pushes to get to Aelita. He then pushes against Aelita to send to Yumi, who sends her flying to the other side. Aelita runs off to the elevator as a Creeper fires at the floating Odd and Yumi. Aelita gets to the computer interface and reactivates control of rebooting the materialization program. He materializes the two as Yumi and Odd about to be devirtualized permanently. Ulrich goes down to the Scanner Room to see that his friends are once again in their original bodies.
At school, Ulrich flips an euro to see whether Odd or Yumi would arrive first. He decides on Odd and he's right. Odd snaps up Ulrich's Euro in mid-air and pops it into the coffee vending machine. Ulrich asks Odd if he told Yumi what happened between them. Odd tells him he doesn't plan on telling anytime soon. Yumi walks up, reading the school newspaper and sees the photo spread inside, depicting Yumi with Ulrich. One can only speculate on the extent of Yumi's rage and Odd's suffering for this heinous injustice.
This episode contains examples of:
- Artificial Gravity: The room the button is in has this, and it takes Odd falling off to notice that it has below-earth gravity.
- The Art of Bra Removal: Odd in Yumi's body feels an itch on his back, and Yumi forcefully shouts at Odd to not take off her bra while they are body swapped.
- Five-Second Foreshadowing: Ulrich plays heads or tails against himself and bets on Odd to come out first, but Yumi does... who is actually Odd in Yumi's body.
- "Freaky Friday" Flip: Odd and Yumi swap bodies for the duration of the episode.
- Forced Friendly Fire: Yumi shoots a laser arrow at Odd to give him some momentum to hit the button to stop the timer resetting the rooms.
- Heroic Sacrifice: What Ulrich does for the rest of the crew before they leave for Sector. He completely blocks a mega tanks' laser, saving the vulnerable Odd!Yumi, Aelita and Yumi!Odd. Ulrich is not happy about it when he materialises back on earth, and beats himself up for it.
- High Heel Hurt: At first, Odd has issues walking in Yumi's Combat Stilettos, made worse by the ice region.
- How Do I Shot Web?: Some of the humor of this episode comes from how badly Odd and Yumi do in terms of using each others' abilities. Yumi can't backflip or aim laser arrows very well in Odd's body, and Odd has trouble aiming Yumi's Tessen fan projectiles, as well as moving about in general.
- Lampshade Hanging: When Yumi gets mad at Odd about the outfit he chose while in her body, Odd reminds Yumi that the clothes are actually hers.
- No Antagonist: The body swapping was a bug in the rematerialization code, not a XANA plot of any kind. XANA only gets involved as his minions roam Lyoko, and he clearly hates the Lyoko warriors being in Sector 5, given what secrets are kept there on how XANA works.
- Out-of-Character Alert: Yumi's mom and dad notice when Odd in Yumi's body uses a fork when they are using chopsticks, and later speaks in Chinese instead of Japanese.
- Say My Name: Yumi screams Odd's name at the end of the episode due to getting a scandalous picture of Ulrich and Yumi hugging together in the school paper.
- Shout-Out: Catwoman gets namedropped by Yumi when getting to Lyoko in Odd's body.
- Simple Solution Won't Work: After the Lyoko Warriors discover a bug in the materialization program caused Odd and Yumi to swap bodies, Odd suggests that they virtualize onto Lyoko and devirtualize back into the real world to fix the problem. Jérémie points out the program could bug up again and leave them without any bodies at all, with Odd conceding the point. In the end, everyone has to wait an entire day for Jérémie to fix the program.
- Third-Person Person: Odd as Yumi speaks this way around William.
- Thinly-Veiled Dub Country Change: The Euro is used in a "heads or tails" game Ulrich plays to guess who comes out of the scanner first. This is a downplayed example, as the game is pretty well known by this name worldwide, so the only reason it's noted here is that the name is being applied to the Euro coin, which just looks weird.
- Voices Are Mental: Yumi uses her own voice in Odd's body, and the reverse is also true for Odd. The lack of any reaction from the characters in-universe indicates that this is purely for the audience's benefit.
