In the courtyard, Odd abandons his and Ulrich's foosball game in order to spend time with Camille, a new girl he is dating. Later, all five Lyoko Warriors convene in Jeremie's dorm room, where they discuss X.A.N.A.'s recent activity. Jeremie announces that he will be giving Ulrich, Odd, and Yumi lessons on how to operate the Supercomputer interface so that they may use it in the event himself or Aelita is incapacitated. Aelita, however, convinces Jeremie to let her skip the lessons in order to compete in the final round of a DJ contest she entered sometime previously to potentially open for the Subdigitals.
In the lab, Ulrich successfully sends Odd to the Ice Sector as part of Jeremie's lesson but Jeremie isn't pleased with the results as he mentions that Ulrich almost hit the wrong button, much to Ulrich's annoyance. Suddenly, however, the Superscan detects an activated tower in the Mountain Sector, and before Jeremie can send Ulrich and Yumi to Lyoko, a polymorphic spectre emerges from wiring in the ceiling and takes the form of a man in a suit. The spectre attacks Jeremie by electrocuting him with a broken cable and knocks him unconscious before quickly escaping from the lab. Still unsure on how to use the interface, Yumi and Ulrich call Aelita, who is in the middle of her audition and does not notice her phone ringing. Ulrich and Yumi tell Odd, who asked them what happened, to look for a way tower to travel to the Mountain Sector. Odd wonders why the spectre left Ulrich and Yumi alone after electrocuting Jeremie and Yumi then deduces that the polymorphic spectre is on its way to attack Aelita, and leaves the Factory to find and protect her.
As Ulrich tries in vain to find a location of a way tower for Odd to travel to the correct sector, three Bloks appear, and Odd is forced to fight them. Odd asks Ulrich to bring him his Overboard so he could fly away from them, but all Ulrich manages to send is the Overbike, which ends up behind the Bloks, forcing Odd to fight his way through. After destroying two of the Bloks and avoiding the third one, Odd uses the Overbike to escape the monster and begins searching for a way tower on his own. Meanwhile, at the audition, Aelita finally notices her missed call, and leaves before the Subdigitals announce the winner. She runs through town toward the Factory, but she notices the spectre among the crowd. Quickly recognizing the danger, Aelita runs away. Yumi arrives a short time later and knocks the spectre into traffic, temporarily incapacitating it and allowing her and Aelita to get to the Factory safely.
While fiddling with the interface keyboard, Ulrich accidentally starts a special countdown. He calls Aelita, who is on her way to the Factory with Yumi, and she informs him the countdown is a delayed virtualization into the Mountain Sector. Considering it a stroke of luck, Ulrich abandons the lab and sends himself to Lyoko. Yumi and Aelita then arrive at the Factory, where it is revealed the spectre has hijacked a car. The spectre attempts to run the girls over on the Factory bridge, but they avoid the car and manage to enter the elevator, returning to the lab unharmed. Odd, who's still in the Ice Sector, notices the tower on the glacier and decides to check it out and after he lands again in the Ice Sector but on a different glacier, finds out that regular towers won't allow to travel into the other sectors. Aelita uses the interface to direct Odd to a way tower on the other side of the ice bridge before having Yumi virtualize her onto Lyoko.
In the Mountain Sector, Ulrich, Aelita, and Odd convene in front of the activated tower, finding it guarded by William and three Krabs. Meanwhile, the spectre enters the lab and begins battling with Yumi. When Yumi stops responding to them, Aelita correctly deduces that the spectre has returned, and Odd volunteers to be devirtualized in order to help Yumi.
Ulrich engages the Krabs while Odd returns to Earth and electrocutes the spectre with a live wire, saving Yumi and causing the spectre to retreat. Aelita then attempts to enter the tower but is blocked by William. Odd takes control of the interface and manages to send Yumi to Lyoko before the spectre returns and attacks him in turn. Yumi arrives at the tower and battles with William while Ulrich defeats the Krabs. When Yumi is devirtualized, Ulrich takes her place fighting William and manages to devirtualize him as well. Aelita then enters and deactivates the tower, causing the spectre to vanish before it could seriously injure Odd. Aelita, Yumi, Odd, and Ulrich then revive Jeremie.
Later, on campus, Jeremie congratulates Yumi, Odd, and Ulrich for being able to operate the Supercomputer competently, and Odd informs the others he has broken up with Camille. Aelita then reveals to her friends that the Subdigitals have called to inform her that she has been officially chosen to open for them at their next concert.
Odd then brings up the attack at the swimming pool. Aelita then asks what happened and Odd said it was similar to the attack at the gym. Jeremie then yells at Odd, telling him he wasn't supposed to bring up the gym attack. Ulrich then asks what happened at the gym, to which Aelita and Jeremie reply that nothing happened while blushing.
- The original French name for this episode is Leçon de choses, which translates to Lessons in English.
- At the beginning of the episode, Odd mentions having broken up with a girl named Melanie. This girl was the inspiration for the code name of the Skidbladnir.
- Jeremie is the only Lyoko Warrior who does not use the Supercomputer in this episode.
- Ulrich virtualizes Odd, and inadvertently, himself onto Lyoko in this episode, marking the only two times in the original series where Ulrich virtualizes someone.
- This is also the only episode in the entire series in which Odd virtualizes someone.
- Ulrich's farewell clip in Echoes was taken from this episode.
- Throughout the entire episode, specifically in all the scenes that take place in the lab, the Holomap shows that Sector Five is the only sector on Lyoko that has been recreated even though the entirety of the virtual world has already been restored by this point.
- When Odd destroyed one out of the three Bloks, there's now only two, but when Ulrich materialized the Overbike, it showed three Bloks on the Factory Interface.
The original summary for this episode can be found here.