After Jeremie and Ulrich paint graffiti portraying Jim in a less than favorable light on a wall in order for Jeremie to remain at school during a vacation, Sissi overhears him talking with the others about his reasons for doing so: namely, watching X.A.N.A... She gets her father to let her stay there during the vacation so she can discover the group's secret. X.A.N.A. takes the opportunity to possess several barrels full of poison and turns it into a deadly, living gas.
When Jeremie finds out, he calls his friends away from their respective vacations. X.A.N.A. uses the gas to attack Jeremie, Jim, and Sissi, and Jeremie just barely makes it out. Ulrich stays behind to find Jim and Sissi while the others go to deactivate the tower. In the end, Jeremie once again sprays graffiti only this time Ulrich helps and it shows Jim as a king, much to Jim's liking.
This episode provides examples of:
- Big Word Shout: Jim wants Jeremie to clean the graffiti off the wall "NOW!" (along with Off-Model facial expression).
- Brief Accent Imitation: Jeremie pretends to be Jim, ordering Sissi to clean the wall, the way Jim ordered him earlier. However, that becomes a Right Behind Me moment and the physical education teacher is not impressed.
- Characterization Marches On: Jeremy is notably lighthearted here, making many jokes at the expense of Jim and Sissi. In later episodes, he's much more uptight.
- Closest Thing We Got: Jim is hopeful that Jeremie will escape the gassed school get help, but Sissi isn't impressed, finding him the furthest thing away from Bruce Willis. When Ulrich is the one to reach where the two are trapped, she's noticeably more elated (though not for long).
- Deadly Gas: XANA's attack of the day.
- Not What It Looks Like: Jim suspects Jeremie of "Sleep Walking", but the blond genius had almost suffocated from the gas.
- Three-Point Landing: While justified on Lyoko, Odd lands in front of Yumi (walking Jeremie) this way on Earth. Instead of being scared, Yumi is glad to see him.
- Too Dumb to Live: Who would put poisonous substances in a school? That would be grounds for OSHA to get on the school's principal for that.
