|Air Date (US)||May 18th, 2007|
|Air Date (France)||August 13th, 2007|
|Written by|| Bruno Regeste|
|Storyboard by|| Paul Beneteau|
|Preceeded by||Final Round|
|Followed by||Double Take|
William Returns is the first episode of Season 4 and the 66th episode of Code Lyoko.
At the start of this episode, Jeremie, having his voice disguised as William's father, phones the principal of Kadic Academy to 'let him know that William will not be not coming back to school because he is going on a trip with him.' Delmas falls for it and then hangs up.
In the factory, Jeremie and Aelita announce to Yumi, Ulrich, and Odd that they had recreated Sector 5 after X.A.N.A. managed to destroy Lyoko. Unknown to them however, X.A.N.A. is busy materializing William in the scanner room.
The following day, Jim confronts Odd about 'Paco, The King of Disco' while Odd is brushing his teeth. He questions Odd why it ended up in the school newspaper. Despite this not being his fault Odd ends up in trouble, and things are not better with the rest of the group as Sissi publically questions William's disappearance. Much to everyone's surprise, and Sissi's chargrin, William appears at school but cannot remember anything at all - only that he was 'somehow devirtualised'. The group's gullible nature proves their downfall as Aelita is kidnapped by a X.A.N.A.-possessed William, and it's up to the Lyoko Warriors to save her.
- The original French name for this episode is Renaissance.
- Lyoko has recreated by Jeremie and Aelita using the data sent by Franz Hopper in Final Round, althought only Sector 5 has been recreated in this episode. The countdown also has removed.
- When William's avatar is seen loading on the supercomputer screen, it showed his appearence from the previous episode; however, when he was virtualized, he had his X.A.N.A.-fied appearence. Likely un-updated as to give William a chance of stealth incase the Warriors tried to give him a Lyoko test. Or because he was given his New suit while Lyoko was destroyed, and just now been revirtualized since.