A Great Day is the fourth episode of Season 2 and the thirtieth episode of Code Lyoko.


The episode begins in Carthage, where Aelita is accessing X.A.N.A.'s data. With the Mantas about to hatch, Jeremie asks Aelita to stop so he can take over. The Mantas then emerge, forcing her to stop. Jeremie brings up the vehicles and everyone hops aboard. While waiting for Jeremie to open up the data stream, Ulrich jumps onto a pursuing Manta and destroys it, but he falls. Odd breaks his fall with his Overboard and everyone escapes the sector. With the data collected, Jeremie thinks he can develop an antivirus for Aelita.

When they get back to Kadic Junior High School, it's late at night. As Jeremie and Aelita talk in a dormitory hallway about Aelita's alias, they are being spied on by Sissi, who records the conversation on her walkman. Meanwhile, in the lab, the computer screen turns on for no reason.

The next morning, on Tuesday, everyone is getting ready for school. Yumi is confronted by her father on why she's out so late. At school, Jeremie tries to cheer up Yumi, telling her it's going to be "a great day".Later in the day, Jeremie is confronted by Sissi, who shows him the taped conversation. She threatens to show her father, the principal, the tape if he didn't tell her what was really going on. In Mrs. Hertz's class, Jeremie tells Odd and Ulrich about Sissi's threat. They are interrupted by Mrs. Hertz, who then drills Odd with questions on photosynthesis.

After class, Ulrich practices Pencak Silat in the gym, hoping to distract Sissi. As Sissi tries to keep up with Ulrich, Odd and Jeremie finger through Sissi's belongings to find the tape. Unfortunately, they are caught red-handed by Herb and Nicholas, who parade them to Sissi. As Sissi walks off, an unexpected time reversion sweeps by, bringing everyone back to Tuesday morning. With a second chance to get at Sissi, Ulrich asks her to join her in practicing Pencak Silat. In class, Odd correctly answers Mrs. Hertz's questions, already knowing the answers from before the time reversion. In the gym, Ulrich tells Sissi that Jeremie and Aelita are crazy, saying," for some strange reason, they think they're virtual people."

At the factory, Jeremie discovers that the data they recovered from Sector 5 allowed X.A.N.A. to take control of the supercomputer's time reversion feature. Immediately after Jeremie locates the activated tower, another time reversion starts, bringing them back to Tuesday morning again. This time, the gang goes over to the factory immediately after class. Aelita, Yumi, Ulrich, and Odd enter Lyoko's Mountain sector, where they are confronted by a squadron of Hornets. Aelita and Odd jump off the path, landing on another path below while Yumi and Ulrich continue to fight the Hornets.At school, Sissi shows her father, the principal, the tape. The principal then calls Odd's parents to find out if Aelita is really Odd's cousin. On Lyoko, Yumi is devirtualized by the Hornets. Ulrich jumps off the edge to meet up with Aelita and Odd as the Hornets pursue. At school, Principal Delmas finds out Aelita isn't Odd's cousin, but another X.A.N.A.-controlled time reversion brings everyone back to the start of the day.

This time, X.A.N.A. possesses Sissi and makes her confront Jeremie. On Lyoko, Aelita has been hiding from the Hornets the whole time, but the others can't help her until Jeremie virtualizes them. Sissi takes Jeremie to the Boiler Room, where she is confronted by Odd and Ulrich. Sissi pulls out a metal pipe and attacks Ulrich. As Odd takes Jeremie back to the Lab, Ulrich and Sissi fight with metal pipes. On Lyoko, Aelita is captured by the Scyphozoa, which begins to drain her memory. Yumi and Odd enter Lyoko and attacked: Yumi destroyed the Hornets with her Tessen Fans, and Odd fired a Laser Arrow at the Scyphozoa, freeing Aelita. Now, the only thing between Aelita and the activated tower was a Tarantula. After a few minutes of fighting, it's destroyed. Aelita deactivates the tower, just moments before Sissi was going to kill Ulrich with her metal pipe. The next day, Jeremie theorizes that jumping back in time increases X.A.N.A.'s power. From now on, they would have to limit time reversions, but unfortunately, it will be difficult. The episode ends showing the entire crew together and Ulrich stating:

"We're going to have to be very careful. The next round is going to be tougher than ever."


  • The original French name for this episode is Un grand jour.
  • It is revealed that time reversions strengthen X.A.N.A. Additionally, Towers cannot be deactivated through the use of a time reversion.
  • X.A.N.A. was seen emerging from two different machines in Sissi's room.
  • This episode marks the first occurrence of X.A.N.A. possessing a human being. He previously accomplished this with animals.
  • It's possible that this episode and Exploration are out of order as this episode takes place after Exploration, but in the beginning, Yumi's father appears to be upset about why Yumi is coming home late. In Exploration, the previous episode, Yumi had told her parents at the end the reason she was coming home late, which would mean that problem would already have been resolved.



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