The episode begins with Odd listening to very obnoxious music while Ulrich is trying to study for an exam (the song titled "Glad When You're Bad"). He claims it's a new song he downloaded from the Internet and nobody knows who wrote it.
After Odd starts urging Ulrich to listen to the music too, an irritated Ulrich tells him that he has to study and leaves their room and goes to Jeremie's dorm to get some quiet and study, where Jeremie is working on a robot. Jeremie greets him and tells him that he will help him to study. Odd continues listening to the music but suddenly faints on his bed as Kiwi jumps around, barking. Kiwi seeing his owner lying unconscious starts getting worried and starts quiely whimping.
Ulrich ends up sleeping in Jeremie's room, but constantly wakes up during the night because Jeremie, it appears, talks in his sleep about Aelita, much to his embarrassment.
In the morning they go to the breakfast, and when Odd doesn't show up in the cafeteria, Yumi tells the boys to check out try to found out what happened to him. They find him in his room, grinning and yet unconscious, leaving Ulrich and Jeremie stunned at Odd’s condition. Panicked, they take Odd to the infirmary. The nurse finds out his pulse is dangerously low and transports him to the hospital urgently, and Ulrich and Jeremie go too.
In the hospital, the doctors find that his blood pressure is dropping rapidly. Ulrich begins to feel guilty. Jeremie contacts Aelita and explains the situation to her. He's still not certain X.A.N.A. has anything to do with this ordeal since it can't attack humans directly. But Aelita warns him that there are pulsations in the Mountain Sector; X.A.N.A. has woken up.
Jeremie and Ulrich head for the Factory. Meanwhile, at the hospital, more and more people arrive in the same state of unconsciousness as Odd, close to paraplegia. The attack is a really violent one…
At the school, Yumi sees Sissi walking phlegmatically and then falling unconscious; she was listening to the same music as Odd: "Glad When You’re Bad" and the sound makes the Japanese girl feel dizzy. She takes her to the infirmary where the nurse is playing some classical music on the radio. When she sees Yumi with an unconscious Sissi, she urges Yumi to come inside. Suddenly, the music on the radio changes to "Glad When You're Bad". Yumi notices that Yolanda has fallen into a coma and now she is certain: X.A.N.A. has created a new song and attacked human beings through their auditory nerves, relaying it to the brain.
Fleeing the music X.A.N.A. is broadcasting on the radio, Yumi joins Jeremie at the factory and explains to him how she discovered the killer music. Ulrich is already on Lyoko in combat with Bloks. One of the four freezes the teen completely with its special eye. Aelita finds herself alone and flees while waiting for Yumi to arrive.
Yumi lands in the middle of the catastrophe in the Mountain Sector and places herself between Aelita and the Bloks. When Ulrich escapes the ice, they defeat the monsters with their combined efforts. On Earth, X.A.N.A. infects all the electrical equipment to broadcast its infected sounds. Millions of people are already lying unconscious everywhere.
In the lab, the music begins to play. Caught off-guard, Jeremie tries to disconnect the sound cable to stop the killer music. It only works for a second, as X.A.N.A. uses the large cables above the lab to keep the music playing. In a final effort, Jeremie enters the coordinates and parameters for the return to the past before falling unconscious on his chair. When Ulrich, Aelita, and Yumi lose contact with Jeremie, Ulrich urges the girls to run towards the tower while he uses his powers to wipe out the remaining of Bloks. Unfortunately, he gets devirtualized by the last Blok and returns to Earth only to be greeted by the killer music playing in the scanner room.
At the hospital, Odd, the first victim, falls further towards cardiac arrest with the goofy smile still on his lips; his electrocardiogram sounds a critical and fatal beep…
The last obstacle on Lyoko, in order to get to the tower, they need to get past a large number of moving rocks. Yumi and Aelita started jumping But Aelita, protected by Yumi, manages to get across. She enters the Lyoko code at the moment when Odd’s life begins to slip away. The return in time engulfs a quiet city, an inanimate school, and a hospital where many bodies lie numb.
Everything goes back to the day before the exam. This time, Odd downloads a different tune called "Under My Cover" by R.U. Clegmatic, which he claims is a song "a machine" would have written. Whom Odd is referring to is none other than X.A.N.A..
- The original French name for this episode is Musique mortelle.
- The song that X.A.N.A. created is called "Glad When You're Bad".
- This is Matthew Geczy's favorite episode, according to Lyoko: Decoded.
- Killer Music was included in "Movies, Music, and Mayhem".
- In the Finnish dub, the episode's name is Tappavan Hyvää Musiikkia, which literally translates to Killing Good Music.
- This episode marks the first appearance of the Hospital.
- This episode reveals that X.A.N.A. can now attack humans directly.
- In one scene, Herb's collar is miscolored green instead of white.
- There are three skateboards at the start of the tunnel when Yumi arrives, even though Ulrich already took his to the factory.
|Code Lyoko: Season 1|
|X.A.N.A. Awakens | Teddygozilla | Seeing Is Believing | Holiday in the Fog | Log Book | Big Bug | Cruel Dilemma | Image Problem | End of Take | Satellite | The Girl of the Dreams | Plagued | Swarming Attack | Just in Time | The Trap | Laughing Fit | Claustrophobia | Amnesia | Killer Music | Frontier | The Robots | Zero Gravity Zone | Routine | Rock Bottom? | Ghost Channel | Code: Earth | False Start|
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