|Air date||December 12, 2013|
|Written by||Josep Maria Roca Peña|
The Big Loss
The episode begins in Kadic, where the Lyoko-Warriors are in a class with Mrs. Hertz and Jim talking about the two World Wars and the weapons that were used. Odd is sleeping, until Mrs. Hertz makes him wake up. Odd quickly says "The result is 42", which has nothing to do with the class. And all students get to laugh. Jeremy tells Aelita that guns are very powerful, and if X.A.N.A. had in his possession a number of weapons that potential, would be able to defeat them and rule the world.
When the class is over, Odd asks Ulrich if he's thinking about Yumi, and Odd says that one day he should be declared. Ulrich says it isn't so easy, and Odd reminds him that William left the Academy, which has a free hand. Ulrich replied that this way of acting that is Odd is what makes the girls won't last more than two days. Then comes Yumi, who explains that in her class she did a French exam. Odd and Ulrich say they had a class about World Wars, and Yumi says she took the same class last year. Then Jeremy and Aelita are worried, and say that X.A.N.A. is doing some strange movements in the network, but doesn't know why. Meanwhile, in an armory on the outskirts of New York, a spectre of X.A.N.A. enters and X.A.N.A. takes possession of all weapons.
The Lyoko-Warriors go to the Factory, and Jeremy types something on the computer and says, "X.A.N.A. has also attended our class". The other four ask what happens, and Jeremy explains that X.A.N.A. has taken control of an armory in New York, so they have to go there with the Translation and prevent X.A.N.A. cause a disaster. The Lyoko-Warriors go to scanners and Jeremy virtualizes them in the Sector 5 of Lyoko. The four go to Skid. Jeremy tells Aelita that they have to go to Xanadu, as the attack comes from there. Aelita does, and they go out of the sector 5 via the mountain sector, and immersed in the Digital Sea.
After crossing a virtual wormhole in the Digital Sea, they enter in the first sector of Xanadu. There they discover that the tower is in a third sector that they haven't seen, and they must cross a tunnel. Aelita go with the Skid through that tunnel, and they find another sector of Xanadu that it's also red and dark but full of hooks on the floor and cannot touch the ground or they will be devirtualized. Jeremy discovers that there is also a tower deactivated, and Aelita connects the Skid in that tower and she says they are prepared. Jeremy says the mission is urgent, which he will send three of them, while one will stay to protect the Skid if monsters come. Ulrich volunteers to stay, and Jeremy sends Aelita, Odd and Yumi to the armory.
In the outskirts of New York, the three Lyoko-Warriors enter the building, and some men are possessed by X.A.N.A. and they start to attack them. Odd said to be responsible for the possessed men, and tells Aelita and Yumi to go ahead. Then Jeremy see on his screen that X.A.N.A. has activated another tower, which will be a surprise. It turns out that the surprise is that X.A.N.A. sends X.A.N.A.-Sissi to the armory, and a blow with his sword devirtualizes Aelita. Jeremy says that could be a benefit to them because Aelita can disable the two towers. In Xanadu, Aelita wakes up and down the Skid. But quickly must use their wings and fly, because they are the hooks on the floor. Aelita goes to first tower, and deactivates it. Thus, the possessed men are unconscious. But there is still activated the tower that X.A.N.A. used to send X.A.N.A.-Sissi to New York.
Aelita leaves the tower, but appear three flying Tarantulas, and when it is almost defeated, Ulrich appears and destroys two Tarantulas, but is devirtualized by hooks. In New York, Yumi and Odd are still fighting against X.A.N.A.-Sissi, and Jeremy say he won't hold long. X.A.N.A.-Sissi uses the pink spirit and devirtualizes Odd, who returns to the Skid. Aelita manages to enter the tower, but she has an idea and she tells it to Jeremy: this tower has the programs which X.A.N.A. uses to control Sissi and they can recover her. Aelita sends the programs to Jeremy and deactivates the tower, and X.A.N.A.-Sissi returns again to Xanadu. In New York it has finished the attack, but in Xanadu appear more flying Tarantulas and X.A.N.A.-Sissi, and they prepare to destroy the Skid. Yumi returns to Xanadu.
Aelita enters the Skid and they go out of Xanadu, and they return to Lyoko. Mission accomplished. And at the factory, Aelita and Jeremy speak with some programs that they can rescue Sissi. The Lyoko-Warriors get excited, but Jeremy says to run these programs they must do another mission to Xanadu, and it won't be easy with X.A.N.A. The Lyoko-Warriors return to Kadic, and the Park are Jim tells them they should be a class, and they have missed classes, they will be punished two hours in the library. Odd says het can make the mission another day, and the Lyoko-Warriors go with Jim to the library. And in the library, Jeremy says that if they do the mission, they will deactivate Sissi's clone, but the real Sissi could cause problems because she discovered the Factory and could tell everything to her father. Odd says he knows how to convince her, and the others are surprised. Odd says he has a plan that never fails, and everyone gets a laugh and the episode ends.