|Air Date (US)||April 22nd, 2004|
|Air Date (France)||September 24th, 2003|
|Written by||Françoise Charpiat|
|Storyboard by||Thomas Astruc|
|Preceeded by||"Holiday in the Fog"|
|Followed by||"Big Bug"|
When Sissi finds and steals Ulrich's diary, he is blackmailed into being her boyfriend. During a trip to a swimming pool, Jeremie and Yumi have the opportunity to find it. The new electric bus that is being used for the field trip is possessed by X.A.N.A., with Odd and Ulrich on board, and starts acting bizarre as a result.
Yumi ends up finding Sissi's diary during this, and uses it to blackmail her into giving up the location of Ulrich's. X.A.N.A. then turns the bus on the city's petrol-chemical plant, threatening to blow up a sizable portion of the city. Yumi is sent to Lyoko to help Aelita but she is devirtualized in the process. Luckily, Odd manages to escape from the bus, leaving him to take Aelita safely to the tower to deactivate it, saving the bus full of students and the petrol-chemical plant.
- The original French name for this episode is Carnet de bord.
- No weapons were used on Lyoko.
- It is revealed that both Ulrich and Sissi have a diary.
- It is shown in this episode that Yumi knows how to pick a lock.
- This was the last English episode with Christine Flowers, since the role of Sissi was transferred to Jodi Forrest. It was also the last episode before Christophe Callabero was replaced by Matthew Geczy, for the role of Odd in the English dub.