XANA has taken control of the assembly line in the deserted factory. Hervé and Jeremy’s droids, which they have made for the school’s Robot Encounters Day, are fighting one another in the gymnasium. Meanwhile, another much more frightening robot created by XANA turns up at the school, creating panic and mayhem. Our heroes have no time to lose. While Odd and Jeremy rush to the laboratory, Yumi and Ulrich try to eliminate the robot which is hot on their tails. But things are not as easy as they seem: the Robot has destroyed the laboratory, which means that no one can get to Lyokô until it’s up and running again, and Aelita is in danger ! What’s more, thanks to its artificial intelligence and reinforced armour, XANA’s Robot seems indestructible. And Jeremy has to stay in the factory to fix the lab ! Out of sheer desperation, Yumi and Ulrich will have to join forces with the enemy : and ask Hervé to help them!

To make decrypting Franz Hopper's journal easier, Jeremy decides to activate a tower once more. But while Aelita is transferring data, XANA tries to take back control of the tower and could possibly gain access to the restricted-access part of the Super-computer where Jeremy has stored all of the data he has collected since the very beginning. Meanwhile, Yumi is trying to find Odd, who has fallen into a trap, while on Lyoko, Ulrich is fighting against a spectre which is a clone of himself...

Jeremy and Aelita, using data sent to them through the network from Franz Hopper, manage to reconstruct part of Lyoko: Sector 5. It would seem that things have taken a turn for the better: the real William reappears at Kadic, apparently unscathed. His unexpected return comes not a moment too soon, because Sissi—who forcefully assumed editorial control at the “Kadic Herald”—has taken a marked interest in finding out more about him. But William, now clearly still under Xana’s control, kidnaps Aelita and absconds with her onto Lyoko…

Jeremy creates a polymorphic specter of himself to go to phys ed class in order to be left to work undistracted on bringing William back from Lyoko. Jeremy’s body double turns out to be far more athletic than the original, to Jim’s considerable surprise. But Xana wrests control of the tower Jeremy used to conjure up his clone, and the imposter now poses a serious threat to our heroes. A battle ensues on the now fully reconstructed Lyoko, featuring new, updated gear for the Lyoko Warriors.

All of Kadic Academy is buzzing: the drummer for the famous rock group, “The Subdigitals”—who just so happens to be the nephew of one of the faculty—is visiting the school. In fact, he is there to hold auditions as part of a promotional operation to discover young musical talent—the winner going on to play the opening set for the Subdigitals’s upcoming concert. Aelita, realizing her gifts as a DJ, would love a chance to audition, but she doesn’t count on Xana’s incessant intentions of kidnapping her…

A recreation lounge room is unveiled for the students at the academy. William’s body double, created by Jeremy to replace the Lyoko prisoner, is elected student manager. Unfortunately, this version of William has a major flaw: he is absolutely daft. With the clone’s erratic stupidity attracting unwanted attention, Jeremy urgently runs a program to try and recover the real youth from Lyoko. But a bug stymies the program and Xana takes over the tower that controls William’s clone.