The episode begins in Sector Five, where Aelita is accessing X.A.N.A.'s data in the Celestial Dome. 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 Academy, 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 refuses to 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 out of the gym, an unexpected return to the past 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 return trip. 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 Five was only a trap as it allowed X.A.N.A. to take control of the supercomputer's return in time function. Immediately after Jeremie locates the activated tower, another return trip starts, bringing them back to Tuesday morning again. This time, the gang heads 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 that Aelita isn't Odd's cousin, but another X.A.N.A.-controlled return to the past 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 attack: Yumi destroys the Hornets with her Tessen Fans, and Odd fires a Laser Arrow at the Scyphozoa, freeing Aelita. Now, the only thing between Aelita and the activated tower is a Tarantula. After a few minutes of fighting, it's destroyed. Aelita deactivates the tower, just moments before Sissi is 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 temporal 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 in this episode that return trips to the past strengthen X.A.N.A.
- Additionally, towers cannot be deactivated through the use of a return in time.
- A spectre 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 and insects.
- This is the first episode in which X.A.N.A. starts his attacks more than one time.
- Near the beginning of the episode, Yumi's father appears to be upset about why Yumi is coming home late and he demands an explanation from her despite the fact that Yumi already told him "the truth" in the previous episode.
|Code Lyoko: Season 2|
|New Order | Uncharted Territory | Exploration | A Great Day | Mister Pück | Saint Valentine's Day | Final Mix | Missing Link | The Chips Are Down | Marabounta | Common Interest | Temptation | A Bad Turn | Attack of the Zombies | Ultimatum | A Fine Mess | X.A.N.A.'s Kiss | Vertigo | Cold War | Déjà Vu | Tip-Top Shape | Is Anybody Out There? | Franz Hopper | Contact | Revelation | The Key|
|Season 1 · Season 2 · Season 3 · Season 4 · Code Lyoko Evolution|