The episode starts at the factory. The gang is planning another trip to the fifth region. Yumi is late for some reason. In the Scanner Room, Ulrich wonders where she might be, Odd guesses that she might be spending time with William. Around this time, Yumi can be seen taking the sewer passage to the factory. She arrives just as Jeremie sends the others to Lyoko. He has them wait while he sends her to meet them.
On Lyoko, Ulrich questions Yumi on why she's late. When he impulsively asks if she was with William, she responds by saying it's none of his business. A small argument breaks out between the two. It doesn't last, however, as some Kankrelats interrupt them. They battle with the Kankrelats for a short while, with each of our heroes managing to take out at least one. Odd manages to hit two. The last one is scared off by the Scyphozoa. A change in tactics by XANA has the Scyphozoa attacking Yumi this time. Ulrich frees her fairly quickly and the monster retreats. Confused by what's happened, Jeremie decides to bring everyone back. He starts with Aelita, Odd and Yumi, but only manages to bring back the first two. He tries again with Ulrich and Yumi, but only get Ulrich back. He sends Yumi to an empty tower while he analyzes the problem. It's at this time that we learn that picture day is today. It seems that the test last episode was the finals for the year. Everyone has been moved up a grade and needs to have their picture retaken. Odd jokes around saying he'll take the picture for Yumi. Ulrich actually agrees, but has a different actor in mind.
At the school, Ulrich asks Sissi to dress up as Yumi. He says he'll do almost anything in return. Sissi agrees, but, surprisingly, wants nothing in return. Roughly half an hour later, she comes out looking somewhat like Yumi, only in a shorter blue dress. When Ulrich points this out, she has him go get one of Yumi's dresses. At the Ishiyama household, Ulrich sneaks in to get a dress. Yumi's parents can be heard arguing in the background. It seems their marital troubles haven't been completely resolved. Ulrich eventually finds the dress.
At the factory, Jeremie runs a scan of Yumi to find out what's wrong. It turns out that the Scyphozoa stole her DNA sequence which is needed to materialize her. Aelita has an idea and has Jeremie send her to Lyoko. Despite Jeremie's questions, she won't reveal her plan to him. Once she reaches the tower, she activates a process that will transfer her DNA sequence to Yumi. Jeremie tries to protest this, but Aelita cuts off the signal. Jeremie's analysis of the process reveals that the DNA transfer will give XANA free access to Aelita's memories. He tries to contact Ulrich to help.
Back at Yumi's house, Jeremie's phone call alerts Mrs. Ishiyama. She enters Yumi's room, but some quick thinking by Ulrich has her believing that Yumi merely forgot her cell phone. Ulrich climbs out of the window once she closes the door. Outside, Odd has been playing a racing game on his Game Boy. Ulrich asks him if he calls that "keeping watch," to which Odd replies that he didn't see anyone go by. They deliver the dress to Sissi and head to the factory.
At the class picture, Sissi tries to blend in with the crowd. William notices that she isn't really Yumi, which catches the attention of the rest of the class. All of their questions alert the principal, who instantly notices his daughter once he arrives. Sissi just says that she has a good reason for it as the photographer captures the scene.
On Lyoko, Aelita has nearly finished transferring her DNA sequence. Odd and Ulrich arrive in time to stop her. After scolding Aelita on her recklessness, Jeremie has another idea. Since XANA stole the DNA sequence, it must be in the fifth region. Once they all arrive, they have three minutes to shut off the timer. The switch can be seen at the end of a path across a canyon. They all realize it's a trap, but Odd takes off anyway. It turns out that the ceiling is booby-trapped and tries to crush Odd as he runs along the platform. Ulrich manages to save him from the first one. They make it over halfway across without incident, but a misstep by Ulrich forces Odd to sacrifice himself to save him. Needless to say, the falling ceiling takes him out of play. Ulrich reaches the switch and shuts of the timer. They all take the elevator to the access panel. While Aelita searches for the DNA sequence, Ulrich apologizes to Yumi for their argument earlier. Yumi reveals that she was buying tickets to another Subsonics concert. They are cut off by the Mantas' attacks. Aelita manages to find the DNA sequence and gets it to Jeremie just before Yumi is devirtualized. Aelita and Ulrich head back out of region now that there's no reason to stay.
In the lab, Yumi has been virtualized safely. Odd is fine, too, but is still reeling from being crushed in Lyoko. Back at the school, Sissi has taken the heat for Yumi's absence. As a gesture of gratitude, Yumi gives Sissi the tickets so she can go with Ulrich. Odd is suspicious of Sissi's selflessness. Aelita thinks that Sissi might actually be a good person, but Jeremie thinks she's just crazy about Ulrich. Odd thinks the whole situation is a mess and the episode ends.
This episode contain examples of:
- Bait-and-Switch: Yumi is briefly captured by the Scyphozoa, allowing it to remove her DNA Sequence; meaning she cannot materialize back on earth. The crew legitimately cannot work out why XANA would do such a thing other than to toy with them. This was a Batman Gambit to get Aelita to transfer her DNA sequence code to Yumi to allow her to return to earth (which XANA likely knew was in her personality) so Aelita would then become completely vulnerable to XANA's attacks and allow him to steal her memory at will.
- Batman Gambit: XANA wants to steal Aelita's memories, but first has to remove the DNA Sequence from one of the warriors and her close friends. When Jeremie finally realizes this, he also realizes that XANA must have her DNA sequence in his own code, and so they go to Sector 5 to retrieve it, itself a Batman Gambit as Sector 5 is completely randomised each time they visit.
- Compromising Call: Jeremie calls Ulrich just as Yumi's mom is about to check in on her.
- HP to One: Yumi is just as vulnerable as Aelita is in this episode, as her life points were stripped away when XANA got her DNA Sequence. If Yumi is devirtualized on Lyoko, she dies for real.
- Just in Time: Jeremie manages to recover Yumi's DNA sequence seconds before she got killed on Lyoko.
- Lampshade Hanging: Sissi is being oddly kind in this episode, and it's not clear why, something which the whole group points out.
- Lost in a Crowd: Invoked by Sissi, but immediately falls flat when William notices that she isn't Yumi.
- No Antagonist: Subverted, as it initially appears XANA's beef with the Lyoko Warriors is by snooping around Sector 5, but otherwise leaves them alone. It turns out this was a Bait-and-Switch, whereby he was to capture one of them the Scyphozoa and remove their DNA Sequence, which means they cannot materialize on earth. This happens to Yumi during this initial beefing session, which is problematic as she has a school photo day to attend.
- Oh, Crap!: Jeremie cannot materialise Yumi, and his reaction is this.
- O.O.C. Is Serious Business: Sissi does Ulrich a solidnote without asking anything in return, even taking the heat afterward, talking nicely to Yumi. Odd lampshades how strangely nice she is. This is never explained in the episode as there appears to be no ulterior motive for Sissi.
- Paper-Thin Disguise: Sissi dresses up like Yumi for a school picture; William quickly notices.
- Picture Day: The episode revolves around Yumi having a school photo, which is treated as Serious Business. If a student is inexcusably absent, they are suspended for a day. Making things worse is that they cannot time travel otherwise they make XANA stronger.
