While Aelita and Yumi are on a mission on the Cortex, a spectre attacks at the school. Odd and Ulrich are unreachable, the girls must double back and deactivate the tower. Unfortunately, Yumi is devirtualised and things become even tougher when Odd has his codes once again stolen by the specter, shortly followed by Ulrich. It's a massacre! Aelita is the only one who can deactivate the tower again.
On Earth, a specter that looks like Mr Rouiller succeeds in draining some of Yumi's source codes and X.A.N.A.'s power reaches 95%. Aelita deactivates the tower, and the specter vanishes, leaving Yumi in a really worried Ulrich's arms.
- The original French name for this episode is Hécatombe.
- The Catalan subtitles for this episode can be found here: Massacre: Catalan Subtitles
- Final apperance of Lyoko in season 5.
- Final tower deactivation in season 5.
- Third and final time Aelita deactivated a tower in season 5.
- The title refers to Odd and Ulrich losing the rest of their source codes, and Yumi losing almost all her codes in the one episode.
- X.A.N.A.'s power has now reached 95%, and Aelita is determined to destroy the Cortex rather than seek her mother out, as the risk is too great.
- Yumi and Aelita are now the only ones left that can deactivate towers.
- This is the first episode that The Skidbladnir appeared in the Mountain Sector.
- This is also the first episode where The Skidbladnir's weapons were used to attack a non-Digital Sea monster.