The episode begins as Odd, Ulrich, and Jeremie are walking down the hallway of the dormitory building. Jeremie is trying to count the number of girls Odd has dated. Odd reveals to them that he has dated all the girls in 8th grade, except for Heidi Klinger. As they walk past Sissi and her group, Sissi asks Ulrich to see a movie called "Adventure in the Tropics" with her. Immediately, Ulrich says he's already seen it and leaves. Sissi is disappointed and Herb Pichon says he'll go with her. Sissi sarcastically agrees, wiping that giddy look off Herve's acne-ridden face. In the Desert sector of Lyoko, a tower activates.
In the shower room, Odd asks if Ulrich really saw the movie and Ulrich responds that he'd rather study for a math test than go on a date with Sissi. Herve, overhearing Ulrich, says he'll knock that "smile" off his face. Ulrich, still calm, tells him to go ahead. Herve then kicks around aimlessly in the air and accidentally karate chops the sink. In pain, Herve retreats from an embarrassing defeat. Jeremie leaves, saying he promised Aelita his croissants for her to eat since she loved eating them with her hot chocolate. In the showers, Odd tells Ulrich that he got a date with Heidi Klinger.
Outside, one of X.A.N.A.'s ghosts emerge.
In front of the Cafeteria, Jeremie walks up to Heidi Klinger. She asks if he's seen Odd since he promised to have breakfast with her, but he grabs her and kisses her rather passionately as Odd and Ulrich arrive and see the whole event. He then runs off. Odd is shocked that Jeremie kissed his date in plain view. Meanwhile, in front of the vending machine, Yumi comes up to Mathias and kisses him while William comes across the scene and watches in obvious shock. As Aelita and Jeremie walk, they pass by Heidi, who asks Jeremie why he kissed her in front of Odd. At hearing this, Aelita walks away from Jeremie who denies such an event ever happening. In the Cafeteria, Jeremie comes to the table where his friends are, but tensions are high. Odd, angry at him for kissing his date, and Aelita, mad at him for kissing another girl, leave immediately. Ulrich gets out of his seat and takes Jeremie's croissant as he leaves, saying he won't be needing the croissant anymore since he intended to give it to Aelita.
As Aelita, Odd, and Ulrich leave the Cafeteria, William comes up to Ulrich and tells him that Yumi's going out with Mathias Durrell. Shocked at the news, Ulrich puts down his croissant as Yumi comes up to them. Ulrich starts grilling her with questions on Mathias. Yumi says that he is nice, and asks why. William bluntly asks, how does he kiss and Yumi, stunned, asks why they were asking her such a question when Ulrich tells her not to deny it as William saw her. Her two pretenders walk away, leaving Yumi confused as to what's going on. She asks Jeremie what the rumor is about her and Mathias. Jeremie then tells her about the rumor that he kissed Heidi Klinger.
Meanwhile, in the bathroom, a polymorphic clone changes from Yumi to Ulrich. Outside, Herve is trying to convince Sissi that Ulrich doesn't want her, saying he said so himself. Unfortunately for Herve, Ulrich walks up to Sissi and kisses her. Jeremie and Yumi then watch the entire event from the distance, leaving Yumi stunned.
In history class, things boil over. Ulrich asks Jeremie why he kissed Heidi, saying it wasn't a very nice thing to do to Odd. Jeremie denies it and when Ulrich states that he saw it, he accuses Ulrich of kissing Sissi in order to get back at Yumi. Ulrich, clearly surprised at the accusation, claims it never happened and Jeremie uses the same reason they did for him with Heidi, telling him he saw him. The teacher goes on with the lesson as Ulrich remains shocked. The teacher, noticing Ulrich's distraction, picks him for a question which Ulrich is unable to properly answer.
Outside, Jim, who is on patrol, sees Ulrich who is supposed to be in class, and chases him. Ulrich runs around the corner and Jim follows him. However, he sees Yolanda Perraudin, the school nurse, passing by. She walks up to him and kisses him, much to his pleasant surprise. After class, Jeremie sees as Aelita kiss Nicholas, who is dumbstruck. Later, Aelita comes up to Jeremie in the Dormitory after being told he wanted to speak with her. He accuses her of making a fool of him in public and of lying to him. Jeremie walks into his room and slams the door. Aelita then runs away. In his room, Jeremie detects an activated tower. He calls Yumi, Odd, and Ulrich - who, meanwhile, is trying to convince Yumi he never kissed Sissi - to tell them about it. He also tries to call Aelita, but she isn't picking up.
In the park, Jeremie explains that all the kissing is because of a polymorphic clone, which can change its identity at will. The purpose: to divide and conquer. This causes Jeremie to realize Odd had been right when saying that "jealousy makes people crazy". Now that they know the truth, all they need is Aelita. They don't know where she is, but Jeremie has an idea.
At the Hermitage, Aelita is moping in the torn-up remains of the upstairs room, the same where Mister Puck had been found. Jeremie comes in and apologizes to her, explaining that it was a polymorph that was responsible for all the drama. He kisses her and they run out of the house, hand in hand.
Outside, they encounter another Jeremie. They accuse each other of being the polymorph. Ulrich, Odd, and Yumi catch up, so they don't know which is the real Jeremie. Aelita begins contemplating and realizes that the real Jeremie wouldn't have kissed her like that and runs over to the other one. The polymorph then grabs Aelita and tries to attack her, but is temporarily stopped by Odd, Jeremie and Ulrich taking him down. Odd stays behind to fight the polymorph as the others take the Hermitage's secret path to the Factory. The fight quickly degenerates into a losing one for Odd, once the polymorph transforms into Jim.
At the Factory, Jeremie virtualizes Aelita, Ulrich, and Yumi into the Desert sector. The activated tower is on the next plateau connected only by a narrow strip of land, which forms a bridge. They begin to run towards it.
In the Hermitage, Odd is getting knocked around. He asks XANA ro turn into a wimp next time. The polymorph obliges his opponent's wish by transforming into Odd. Odd is not pleased. The polymorph proceeds to beat him up even more.
On Lyoko, Aelita continues towards the tower, while Yumi and Ulrich fight an approaching swarm of Hornets. X.A.N.A sends a Tarantula to fight them. Immediately after Aelita runs across the bridge to the next plateau, X.A.N.A deletes it, separating her from the other two. Meanwhile, the polymorph runs across the bridge, into the Factory.
Yumi fights the Tarantula while Ulrich fights the Hornets. However, they have trouble and decide to swap enemies. Jeremie brings up the Overwing and Yumi hops aboard, with the Hornets in pursuit. She throws her tessen fan in a circle around her, destroying the Hornets. Ulrich uses Super-sprint to get behind the Tarantula, but loses his advantage when two more Hornets show up. Yumi swings by to attack the Tarantula, but she is shot down and devirtualized by laser fire. Ulrich destroys one of the Hornets, but he still has two more monsters to go. Yumi comes out of the Scanner and waits at the door as the elevator is in use.
On Lyoko, Aelita is trapped as her escape route has been deleted by X.A.N.A. The Scyphozoa arrives and begins to take her memories. In the elevator, the polymorph Odd transforms into Yumi to coincide with her return from Lyoko. Jeremie brings up the Overbike so Ulrich can cross the gap and get to Aelita. The polymorph Yumi comes into the Lab and tosses Jeremie aside.
Outside, the real Odd has come to get revenge. The polymorph Yumi devirtualizes the Overbike before Ulrich can get on. Instead, he uses Super-sprint to jump across the gap. Meanwhile, Odd arrives in the Lab to see two Yumi's. One of them calls Odd a pea-brain. Odd turns and faces that Yumi, but when it seems they're about to fight, they turn and attack the other Yumi. They knock out the polymorph temporarily and get Jeremie. On Lyoko, Ulrich throws his katana like a boomerang, severing the Scyphozoa's tentacles and returning Aelita's memories. As Aelita enters the tower, the polymorph reawakens. It tosses Yumi and Odd aside and is coming for Jeremie. As Jeremie gets electrocuted by the polymorph, Aelita deactivates the tower. The polymorph turns back into a spectre, which rises up and disappears into the Lab's ceiling.
In the Infirmary, Jim is offering Yolanda Perraudin a flower. She is slightly flattered, but she explains that she is engaged to be married. Jim then asks why she kissed him if she is engaged. Yolanda, confused, asks if she really kissed him. He responds by nodding up and down like a fool causing her to think he must be ill and instructing him to get on the bed so she can take his temperature, much to his disappointment.
Outside, Yumi asks Odd how he knew she was the real Yumi. Odd tells her that only the real Yumi would call him a pea brain not XANA since he has too much "respect" for him. Jeremie then claims he just doesn't know him like his friends do. Aelita then asks Jeremie if he could come with her for a moment. Jeremie is happy to oblige and is met with a kiss from Aelita. He remains in that frozen pose long after Aelita walks away and his friends laugh in amusement.
This episode contains examples of:
- Bait-and-Switch:
- When Jeremie questions where Aelita went after they all had a fight, he goes straight to the Hermitage, and the camera cuts to the two meeting relived. The next scene has Jeremie notice XANA!Jeremie had already gotten to her first.
- Odd looks as if he's about to punch Yumi, when in fact Odd fully intended to punch XANA!Yumi, which regular Yumi picks up on.
- Be Careful What You Wish For: Odd, as he's getting a beat down by the polymorphic clone that keeps changing into different people, asks XANA to "Turn into a wimp next time". XANA then changes into Odd himself.
- Big "WHAT?!": Ulrich's reaction to hearing how "Yumi" kissed and is supposedly dating Mathias Durrell. When she denies it, he and William storm off angrily.
- Brick Joke: Jeremie wants to give Aelita a toasted croissant and hot chocolate before they all go to class. The next day, when XANA!Jeremie is seen kissing Heidi and runs away, Real Jeremie is heading for the cafeteria, and is left confused by everyone's disdain for him, and Ulrich says that "he won't need that croissant anymore", and takes it.
- Chekhov's Gun: In the end, Aelita asks Jeremie to come over to her so she can check something, that something being how Jeremie reacts to being kissed by her (not smoothly). This directly mirrors how she exclaims outside Hermitage that "he would never kiss me like that", and this was her way of checking if she was correct.
- Distracted by the Sexy: This was how the polymorphic clone manages to get away from Jim when he spots it with Ulrich's appearance, by transforming off-screen into the school nurse, Yolanda to kiss Jim on the cheek, not that this bothers him.
- Five-Second Foreshadowing: XANA!Jeremie pulls off a very convincing Jeremie impression to both Aelita and the audience, even when the two Jeremies meet. The only giveaway is that in the previous scene, XANA!Jeremie kissed her before leaving the Hermitage, and Aelita figures out that Jeremie would never do this, even under a stressful situation like this because A: He's way too shy to try and be that spontaneous, and B: even if he were, he would certainly ask her first.
- KidAnova: Odd reveals he's managed to date almost every girl in the eighth grade except one.
- Love Makes You Stupid: The premise of the episode, with Odd even quoting this early on in the episode as a foreshadow. XANA makes a polymorph clone that can shapeshift to look like anyone at will, and uses it to impersonate one Lyoko warrior kissing a random person in full view of another Lyoko member. All in order to drive a wedge in the group. The bickering does go on for a long time, and Aelita runs away to Hermitage when Jeremie snaps at her when seeing "her" kiss another guy. It takes Jeremie noticing the tower scan had picked up an activated tower for everyone but Aelita to come to their senses. They mention how tricky XANA has gotten in playing on their emotions and Jeremie remarks Odd was right in that "love makes you crazy".
- Malaproper: Odd mistakes the word "polymorphic" with "poly-dorking" until Yumi corrects him. He stops trying the second time he gets it wrong; "poly-whatever".
- Manipulative Bastard: XANA uses the team's personal romantic feelings for others against them. This is, by far, one of his strangest plans since it involves a polymorph clone changing forms and kissing random characters in order to separate Aelita.
- Master of Disguise: The polymorph is near-perfect, and the only weaknesses it has is being too hasty in some of its actions, such as XANA!Jeremie kissing Aelita when Jeremie would never do such a thing without asking first.
- Mistaken for Cheating: The central plot of this episode, planted by XANA, see Love Makes You Stupid for why.
- NOT!: Sissi throws this on Herb when he wants to go to the movies with her in Ulrich's place.
- Nice Job Breaking It, Hero: XANA gets the idea to start lover spats from overhearing Odd talk about how he's dated almost every girl in his grade, and Ulrich mocking Herb for trying to fight him over jealousy with Sissi.
- Post-Kiss Catatonia: Under the guise of "checking something", Aelita gives Jeremie a full-blown kiss in front of everyone in the final scene before smoothly walking away. Jeremie is seen frozen in an awkward sort-of running pose as she casually comments that she was "right". Odd jokes that it's gonna take a while for him to recover.
- Spot the Imposter:
- Aelita spots the fake Jeremie when he reveals he kissed her. However, Aelita says the real Jeremie would not kiss her like that (especially without her express permission), and the gang starts dog-piling onto him to restrain XANA!Jeremie.
- Yumi asks Odd how he knew she was the real Yumi. Odd tells her that only the real Yumi would call him a pea-brain not XANA since he has too much "respect" for him. Jeremie just counters by saying that XANA doesn't know him that well.
- That's Gotta Hurt: After Herb smashes his hand into the metal communal sink, Ulrich says, removing his toothbrush from his mouth between words, "Ouch. Now that has gotta hurt."
- What the Hell, Hero?: It all starts off with Heidi (and later Odd, and even later on, Ulrich) blaming Jeremie for kissing her. Aelita walks off in disdain. William and Ulrich each blame Yumi for kissing Mathias. Then the tables flip on Ulrich when he is blamed for kissing Sissi. To top it off, Jeremie then hurts Aelita when it appears she kissed Nicholas. Subverted in that this was all XANA's doing, and they all calm down pretty quickly once they reunite in the forest.
