The Key.After going through all of Franz Hopper's diary, Jeremy discovers the truth behind the Supercomputer, at least to some extent. Hopper has used it quite extensively, to the point of repeating a single day for more than seven years. His sanity degraded throughout the experience. Hopper also revealed that he and Aelita hold the Keys to Lyoko, which were what X.A.N.A. is after. He only needed her half, now. The Keys would allow him to escape the Supercomputer. Jeremy also finds a way to free Aelita from the Supercomputer. It turns out that Aelita never had a virus. In fact, X.A.N.A. has been holding onto a piece of her, which is responsible for linking her to the Supercomputer. Aelita is not willing to go, angry over the fact that Hopper has essentially taken her life from her. She's also worried that X.A.N.A. might escape. To that end, she shuts down the Supercomputer. Jeremy rescues her, and the group goes to Lyoko to retrieve her fragment. After all their efforts, they seem to succeed, but it turns out to be a fake. X.A.N.A. manages to devirtualize Aelita's defenders and steal her memory, effectively killing her and allowing him to escape, which shuts down Lyoko in the process. After his escape, Franz Hopper revives Aelita and Lyoko, restoring all of Aelita's memories in the process, but at the price of Franz Hopper remaining permanently trapped inside the Supercomputer. Through the restoration, Aelita finally remembers her past up to the point that she went to Lyoko. With X.A.N.A. now free and Aelita's memories returned, neither are linked to the Supercomputer. This means that they could shut it down, but it would do no good. Unsure of how they'll proceed, Jeremy promises that they'll find a way to stop X.A.N.A..