It's been a year since the group first discovered the supercomputer and Aelita, so they decide to throw Aelita a surprise party. Sissi catches wind of the party, and follows Ulrich and Yumi to the factory to snoop. On the way there, X.A.N.A possesses the factory as a whole. Jeremie and Odd are the first to arrive at the factory, finding the elevator to be inoperable. They head off to find the fuse box. Once Ulrich and Yumi arrive there, Sissi confronts them about their plans. They tell her to leave, but X.A.N.A's earlier possession allows him to trap all three in the elevator and drop them to the bottom of the shaft. Sissi and Yumi come out okay, but Ulrich's arm is broken in the fall, so Yumi has to go up to the scanner room alone.
Meanwhile, Jeremie and Odd have to deal with the possessed factory equipment. Odd, Yumi and Jeremie manage to make it safely to the supercomputer room, but while Yumi and Odd are getting virtualized, water from the pipe lines inside the walls is falling inside the elevator, with Ulrich and Sissi still stuck inside. When the elevator is filled half way, Ulrich promises to Sissi that if they make it out alive, he would be nicer to her. Just as Ulrich and Sissi are about to drown, Aelita deactivates the tower and the return to the past is initiated to save them both. And just like Ulrich promised, he was nicer to Sissi in the end. The surprise party did eventually go as planned.
This episode contains examples of:
- A Birthday, Not a Break: This episode marks one year since the heroes turned on the Supercomputer and met Aelita. They attempt to surprise her with a small celebration for her "birthday", but they are disrupted by XANA's attack. They are able to celebrate after the Return to the Past, however.
- "Die Hard" on an X: XANA tries something different here, turning the usually-safe factory into a death trap by reawakening the equipment.
- Drowning Pit: The elevator becomes one after the water starts to leak in, nearly killing Sissi and Ulrich.
- Early-Installment Weirdness: Yumi is noted to have a fear of heights that is never brought up again afterward. In Season Two and onwards, it's Ulrich who has vertigo symptoms.
- Everything Trying to Kill You: XANA tries this on Jeremie and Odd, mercifully they both get out OK.
- Evil Elevator: XANA controls the elevator when Sissi, Yumi, and Ulrich get inside.
- Elevator Failure: Ulrich, Yumi, and Sissi are stuck in an elevator. Ulrich stays to comfort Sissi, while Yumi escapes and goes to find Jeremie to help Aelita deactivate the tower.
- Hidden Depths: Sissi creates a makeshift cast for Ulrich's broken arm and tends to him in the elevator, revealing a nicer side to her.
- Injured Limb Episode: Ulrich cannot climb out of the elevator with Yumi as he broke his arm when the elevator fell, so he stays behind with Sissi instead.
- Ironic Fear: This was not the right time for Yumi to confide in Ulrich that she was afraid of heights.
- No OSHA Compliance: Enforced by XANA, who uses this exact thing to kill off the cast with the equipment found in the factory, breaking the boiler room, disabling the elevator, and flooding the elevator.
- Stock Footage: Jeremie and Aelita's talk at the beginning is recycled from "Cruel Dilemma" just before the bulldozer attack plus the montage of Jeremie's schoolday is lifted from "Seeing is Believing" and "Satellite" respectively.
- Took a Level in Badass: Aelita manages to defeat more than one of the enemies on Lyoko by using her wits, first by removing the floor underneath one, and the second by sliding underneath to get to the tower.
