|Air date||November 4, 2009|
|Written by||Josep Maria Roca Peña|
X.A.N.A. in School
The episode begins with Sissi that has succeeded another GPS to one of the Lyoko-Warriors, and discovers the secret again. Meanwhile, Aelita has another nightmare with Franz Hopper and tells it to Jeremy. Later, Odd suggests going to a movie of cavemen, but Yumi doesn't want, and then propose to do a party with Aelita as DJ. She goes for the inputs, while thinking of his father.
While Aelita, Odd, Ulrich and Yumi are at the party, Sissi finds the supercomputer and open it, and Aelita then faints. In the Factory, something attacks Sissi… The next day, in class, the Lyoko-Warriors are talkin about Aelita has fainted, and Mrs. Hertz calls attention to Odd, saying silly. Outside, Aelita thinks X.A.N.A. is awake but Jeremy doesn't believe her. At that time, some motorists who were already at the factory in "Dog Day Afternoon" are possessed by X.A.N.A.. Aelita thinks there's something odd about Sissi, and goes to the Factory.
At the factory, Aelita finds that the supercomputer is on and calls the rest. Yumi, who was with William, leaves, but Sissi is hidden… Yumi comes to the Factory and finds the possessed motorists, while Jeremy virtualizes Aelita. Odd and Ulrich then appear, ready to be virtualized too. In the ice sector, appear Mantas. Jeremy virtualizes the vehicles, but a Polymorphic Clone of X.A.N.A.-William appears too. While Yumi is fighting against the motorists, X.A.N.A.-William pulls Aelita into the Digital Sea, but Jeremy reveals that she has a new power: she can return up to 5 seconds in the past. X.A.N.A.-William devirtualizes Odd, and a Blok launches freeze ray into Aelita.
X.A.N.A.-William devirtualizes Ulrich but he's devirtualized by Aelita. She enters into the tower and off it, and return to the past to know who on the supercomputer. After this, the group goes to the factory, and when the gang discovers Sissi, and she makes a return to the past. When she is almost to activate the Time Reversion again, the Team Lyoko force her to leave the Factory. At the end, Sissi says she won't do the time reversion, and suddenly everyone believe her…
These Time Reversions made X.A.N.A. stronger and sticks another virus that makes Aelita cannot shut down the supercomputer. Jeremy thinks he can fix it soon. The episode ends with a reminder which Aelita is saying "Fighting X.A.N.A. is my job". Jeremy responds, "No, Aelita… it's our job".