After showering in the morning, Ulrich goes to wake up Jeremie, who has fallen asleep at his desktop while working on a recovery program to free William from X.A.N.A. Once awake, Jeremie claims to have finished the program, and plans to launch it that afternoon. In the cafeteria during breakfast, the principle announces the opening of a rec room on campus, and that a monitor is to be elected to take charge of the room's upkeep.
During the impromptu election, the William Clone is inadvertently made rec room monitor, and the Lyoko Warriors worry the Clone may be discovered due to the increased attention being placed on it. After classes, Jeremie and Aelita go to the Factory to launch the recovery program while Yumi, Odd, and Ulrich attend the opening of the rec room to watch over the William Clone.
In the Factory, Jeremie launches the program using the tower controlling the William Clone, but quickly discovers a bug. The bugged program alters some of the files stored in the tower, and the William Clone's personality changes from dim-witted but nice to rude and aggressive. Because deactivating the tower would cause the William Clone to vanish in front of all the students in the rec room, Aelita volunteers to go to Lyoko alone and sort the problem out manually in the tower itself. Jeremie reluctantly agrees, and sends her to the Desert Sector.
Once on Lyoko, Aelita finds she cannot enter the tower because her identification file is one of the files bugged by Jeremie's program. While Jeremie and Aelita discuss whether or not he should manually devirtualize her, three Tarantulas arrive at the tower. Aelita moves to take shelter in a different tower, but when Jeremie discovers X.A.N.A. is trying to gain control of the bugged tower, and thus the William Clone, she circles back around to battle the Tarantulas.
Meanwhile, in the rec room, Jim and the Clone play a furious game of table tennis. Yumi receives a text message from Jeremie asking her, Odd, and Ulrich to come to the Factory, but as they turn to leave, X.A.N.A. succeeds in overtaking the bugged tower, and the newly possessed William Clone attacks them. The trio agrees to slip up, and the Clone targets Ulrich.
On Lyoko, Aelita battles the Tarantulas until she spots William, who appears to be fighting three Krabs. Assuming Jeremie's bugged program worked after all and William is no longer under X.A.N.A.'s control, Aelita saves him from the Krabs. Meanwhile, Yumi and Odd manage to reach the manhole in the park and proceed to the Factory while Ulrich and Sissi (who insists on following Ulrich) are chased onto the roof of the school building by the Clone.
The William on Lyoko then reveals himself to still be under X.A.N.A.'s control. He knocks Aelita unconscious and hijacks the Overwing, planning to dump her into the Digital Sea. Yumi and Odd arrive at the Factory and are sent to Lyoko. Odd rescues Aelita and escorts her back to the activated tower while Yumi confronts William.
On the roof, the Clone catches up to Ulrich and Sissi. Ulrich experiences vertigo and tenses up, forcing Sissi to defend him by throwing shingles at the Clone. Once Ulrich regains his composure, he attempts to fight the Clone, but is knocked off balance and nearly falls off the roof, dangling from a gutter by one hand. Sissi manages to throw the Clone off the roof, but falls as well, and is caught by Ulrich. Meanwhile, on Lyoko, Odd and Aelita battle the two remaining Tarantulas guarding the tower while Yumi is defeated by William and is devirtualized.
In the Lab, Jeremie manages to fix Aelita's identification file, allowing her to enter the tower. However, before she can do so, William catches up with her and attempts to throw her into the Digital Sea a second time. Odd intercepts William, allowing Aelita to escape into the tower while he is devirtualized. Meanwhile, the William Clone returns to the roof and attempts to loosen Ulrich's grip on the gutter.
Aelita deactivates the tower, causing the William Clone to vanish. However, Ulrich loses his grip nonetheless, and he and Sissi fall. They are saved from hitting the ground when Jeremie performs a Time Reversion. The return to the past brings the Lyoko Warriors back to the election, where they deliberately favor Sissi and allow her to become rec room monitor. As the students disperse for morning classes, Jeremie promises that he will bring the real William back to Earth one day.
- The original French name for this episode is Double foyer.
- Two episodes ago, the tower controlling the William Clone is located in a crater in the Desert Sector. In this episode, and every subsequent episode where it is shown, and tower is on the edge of a platform.