This episode starts with Ulrich and Odd at the drink machine. Ulrich is trying to remember formulas for their science final the next day and Odd is not helping. Odd is more worried about the afternoon snack then about studying because he has a plan for success: a cheat sheet. Ulrich would rather study and goes to leave, but an excited Sissi gets there with great news before he can get away. After telling Odd that her news has nothing to do with the break-up of the band Love Potion, she tells them that her father approved the use of the gymnasium for the party. Upon hearing this, Odd gets excited and goes off to find William.
In the gym, Jim is directing the preparation of the gym for the party. While giving the students orders, William trips and the mixing board he is carrying falls out of his hands and breaks. As William bends over to assess the damage, Odd arrives for confirmation of Principal Delmas' approval from William. William tells him it was and Odd becomes excited, saying that all the best DJs from the local schools will be there. William rains on his parade by telling him that no one will be blasting anything because the mixing board is broken and he can't seem to fix it. As William struggles with some of the wires, Odd gets the idea to ask Jeremie because "he can fix anything."
When Odd goes to ask Jeremie if he will fix the mixing board, Jeremie turns him down, telling him he has better things to do with his time. Aelita looks up from what she is reading and offers to help Odd but Jeremie reminds her about the research on her antivirus. Aelita tells him that currently she is only watching him work. With that, Aelita goes with Odd to see if she can fix the mixing board. Before Odd leaves, Jeremie asks him about the science final and Odd responds that it is "in the bag."
In the gym, Aelita is fixing the mixing board and asking questions about it to Odd and William. Odd explains to her how it works. William comments about Aelita's apparent lack of knowledge on the device and asks how much longer. Aelita tells him she's finished and William asks to try it. He puts a record on and discovers that it is in fact working. He offers Aelita a chance to try and she accepts, taking the headphones from him. Aelita tries it and William is amazed by her talent. During the middle of her try, Jim cuts of the power to the mixing board and calls them goof offs, but Odd explains that they were simply rehearsing. Odd asked Jim if he likes techno and Jim says that he dislikes electronic music and prefers the twist. As the three of them are leaving, William asks Aelita where she learned to play so well. Before she can answer, Odd explains that it runs in the family. William offers Aelita a chance to be DJ the next night and she accepts.
When she tells Jeremie about her plans, he tells her she is wasting her time. A big fight is started over this in which Aelita says she just wants to live like the rest of them. Jeremie is shocked to discover she doesn't have a fun time researching the anti virus with him and his comment only makes her more angry with him, saying he is as "stubborn as a fool." As she storms out, Jeremie yells out to correct her.
The next day, Ulrich and Odd arrive to take their science final and Ulrich is surprised to find out that Odd hadn't studied at all. Odd reassures him by telling him its in the bag. As they go to enter the class, they find a line. Odd asks Sissi about it and she tells him Jim is inspecting them. Jim tells the students they will only be allowed to bring in one pen. Odd doesn't seem to worried but does comment that it was unexpected. Mrs. Hertz tells them they will have two hours for physics and two hours for chemistry as she hands out the exams. She explains that herself and her fellow science teachers will grade the exams that afternoon and after which Principal Delmas will announce the results. Then she tells them they can start. Jim walks about the classroom as the students take their exams. Sissi and Odd are not taking their exams seriously as Odd has begun folding his exam while Sissi has been doodling on hers. When time is up, Jim goes around to collect them, telling the students to stay seated until he has all of them. When he picks up Odd's, it is no longer a test but a paper swan. Jim comments on it, calling it one of his "best yet."
As Jim goes to put the completed tests in Mrs. Hertz's locker, he talks to himself, hoping she will let him keep Odd's paper swan for his collection. As he closes her locker with the tests safely inside, X.A.N.A. possesses him.
That night at Kadic, Yumi meets up with Odd and Ulrich in the line to get into the party in the gym. She asks them about the exam and Odd admits that he might get left back a grade. Yumi tells him not to exaggerate but that he should have studied some. Ulrich tells them it's not the time and Odd changes the subject, saying they are going to get to see Aelita the DJ. When he asks where she is, Ulrich tells him that as a DJ, she's already inside. Yumi asks about Jeremie and Odd tells her that he's sulking.
As Jeremie passes Sissi's room, he overhears her father telling her that she cannot go to the party because of her bad science exam. She begs him but he doesn't budge. Jeremie chuckles and continues on, unaware that an X.A.N.A. possessed Jim is following him. Once inside his room, Jeremie sits down in his computer chair. He discovers an activated tower in the desert sector but when he goes to call the others, the X.A.N.A. possessed Jim attacks him.
In the gym, Milly and Tamiya try to interview Aelita about her music. Before Aelita can answer, William saves her by explaining that she is too nervous to answer and explaining that her style is more hard core but also her own. Just then, Sissi arrives and makes her way over to Nicholas and Herb. They ask her if she snuck out and she sarcastically answers that her father told her that she was going to repeat the year but that she should have a good time. Nicholas falls for it and Sissi tells him that she did sneak out.
In Jeremie's room, Jeremie is struggling to get untied as his phone is ringing.
Back at the party, Aelita is announced and she begins to play. The crowd loves her, especially her friends. Yumi asks Ulrich to dance and they do. William goes over to Odd and tells him that his cousin is incredible, to which he agrees.
Back in Jeremie's room, Jeremie manages to tip over his chair and remove the tap from his mouth with one of the legs from his desk. Jeremie starts calling for Kiwi, who is asleep on Ulrich's bed in his and Odd's room. After much screaming on Jeremie's part, Kiwi wakes up and heads to Jeremie. Once Kiwi arrives, he goes straight to Jeremie. Jeremie asks him to chew through the ropes but instead Kiwi just licks his face and walks out, causing Jeremie to comment on both Kiwi and Odd's IQ.
At the party, everyone, even Sissi, is loving Aelita's music. Sissi sees Ulrich dancing with Yumi and decides she wants to dance with Ulrich, something neither Yumi nor Ulrich is happy about. Ulrich tries to ignore Sissi but she just gets more in the way and irritates them even more.
In Jeremie's room, Kiwi has returned with a ball. Jeremie tells Kiwi to go get Odd and the others. Kiwi runs off but Jeremie isn't reassured that Kiwi will listen.
At the party, Aelita is still playing. Odd asks William why he isn't dancing. He tells Odd that dancing isn't his thing. Odd tries to tell him that he can't be that bad but changes his opinion once William gives him a demonstration. Odd hears barking and likes the sound, wondering where Aelita got them, not having realized it was Kiwi. Kiwi eventually gets Odd's attention. Odd asks Kiwi why he's come and Kiwi tries to lead him away. Odd follows but not before running into Yumi. He tells Yumi what he's doing and she comes along. Ulrich hears them and makes up an excuse so he can leave with them and get away from Sissi. After the three of them leave, X.A.N.A. possessed Jim walks in and uses his electrical powers to shock Aelita from across the room by sending an electric shock through the wiring, starting from the power box.
In Jeremie's room, Kiwi is playing with some rope now that Jeremie is untied. Jeremie explains that Jim has become possessed and becomes worried when Ulrich tells him that Aelita is in the gym.
In the gym, Aelita is out cold on the stage and Jim picks her up, saying he'll take her to the infirmary. The party continues as Jim leaves. The gang just misses Jim and Aelita as they run toward the gym. Jeremie tells the rest of them that under X.A.N.A.'s control, Jim can do anything. They become concerned about Aelita going solo against the Scyphozoa. They get inside the gym to find that Aelita is no longer at the mixing table. They see that Jim and Aelita are no longer there and head for the Factory.
At the Factory, Jim is carrying Aelita over his shoulder. He jumps down from the top level without even using the ropes then enters the elevator. Meanwhile, the rest of the gang is just getting on their skateboards in the sewer. Back at the Factory, Jim has placed an unconscious Aelita in a scanner. The gang is still in the sewers when Jim virtualizes Aelita onto Lyoko. Once there, Aelita finds herself facing a Megatank in the crater. The gang gets to the Factory just in time to find Jim getting off the elevator from the lower level. Ulrich tells Jeremie and Yumi to go down the corridor while he and Odd take on Jim. X.A.N.A. copies Jim so that there are two Jims taking on Odd and Ulrich. Ulrich and Odd make the first move but do no damage. The Jims have little trouble knocking them to the ground. Meanwhile, Jeremie and Yumi have managed to make it into the Lab. Jeremie checks in with Aelita and tells her that help is on the way.
On Lyoko, Aelita is planning to attempt to escape by running up the ramp. The Megatank strikes in front of her causing the ramp to break and for Aelita to fall back down.
Back at the Factory, the two Jims have merged into one. Odd wakes up Ulrich and tells Ulrich his plan on how to knock Jim out. Odd then gets Jim's attention and while Jim's back is to him, Ulrich hits Jim with a metal pipe. Once Jim is down, Ulrich and Odd get on the elevator and head down. Jeremie sends them directly to the scanner room. After the elevator takes off, Jim wakes up. From Lyoko, Aelita asks Jeremie to hurry and Jeremie virtualizes Ulrich, Odd, and Yumi. They arrive by the big rocks and Jeremie gives them their directions along with their vehicles. XANA sends Hornets to the three of them and Odd offers to fight them while Ulrich and Yumi go save Aelita. Ulrich and Yumi get on their vehicles and fly away while Odd destroys one of the Hornets then takes on the rest from the rocks. Odd quickly is down to ten life points and still two Hornets remain. The Hornets head toward the crater and Odd follows him on the Overboard. Ulrich gets hit by the Hornets and falls off the Overbike. Yumi turns around to help him but he tells her to continue. She does and Ulrich takes on the hornets, son receiving help from Odd. Odd manages to lose the Overboard and hitches a ride on the Overbike with Ulrich.
In the crater, the Scyphozoa has finally arrived. Just then, Yumi arrives. The Megatank attacks and Yumi manages to get out of the way but the Overwing gets destroyed. Yumi manages to get destroy the Megatank during its next attack but she gets devirtualized in the process, leaving Aelita alone with the Scyphozoa. The Hornets are still on Odd and Ulrich's tail as the Scyphozoa picks up Aelita and begins to steal her memory.
Back in the Lab, Jeremie is beginning to worry. He tells Ulrich and Odd to hurry up and that the Scyphozoa has Aelita. Then Jim comes through the elevator door and takes over control of the supercomputer away from Jeremie and devirtualizes Odd. After getting hit by a Hornet, Ulrich and the Overbike speeds into the crater. He makes it to the bottom just before the Hornets destroy it. Ulrich asks Jeremie about Aelita's memory but gets no answer. After destroying one of the Hornets, he asks again and does not receive an answer.
In the Lab, Jim is attacking Jeremie. Jim is distracted when the elevator doors open and Yumi comes out. Seeing Jim, Yumi attacks. Jeremie is able to regain control of the supercomputer while Yumi fights with Jim.
On Lyoko, Ulrich takes out the last Hornet. Throwing his sword, Ulrich manages to cut off the Scyphozoa's tentacles. Damaged, the Scyphozoa retreats and lets Aelita down. Ulrich and Aelita get to the tower. In the Lab, Jim has knocked Yumi out and turns his attention to Jeremie. Aelita reaches the interface at the top of the tower and enters the code and deactivates the tower. Jim becomes unpossessed and remains conscious. He wants to know what he is doing there but Jeremie launches a return the past.
Back to the day before, Odd is making Aelita and Jeremie promise to help him study for the science exam until he gets it. Then Sissi comes along with her great news. Odd "guesses" that her father approved the gym for the party. Sissi asks how he knows and he tells her that he has already lived through the day and traveled back in time. Sissi calls him looney and he still offers to let her study with them. Sissi declines and walks away. After she's gone, Aelita has Odd promise to teach her all about techno after the exam. After he does, she asks Jeremie if he'll come hear her play and he says he'll be there.
- The original French name for this episode is Mix final.
- It is now revealed that the Scyphozoa must physically travel to its destination.
- Which alludes to the theory of only 1 Scyphozoa ever made.
- This episode shows that Aelita is an amazing DJ player.
- In one shot, one of William's sleeve was miscolored black and the other was gone.
- Ms. Hertz's glasses are darker in this episode.