The episode starts with a movie being shown to the students of Kadic. It involves an evil alien attacking a young woman. The alien is shot down by the main protagonist of the film, and the movie ends with the two humans in each other's arms. Jeremie claims the film to be idiotic, Ulrich thinks it was cool, Odd liked the special effects, and Yumi thinks it was scary. Then Mr. Delmas comes up an announces that the director and writer of the movie, James Finson, is present. Finson informs the students that he will be using an old factory nearby for his newest movie, also a blend of science fiction and horror. Jeremie, scared that the Supercomputer will be discovered, talks to the gang about it. Ulrich says he'll talk to Finson.
Meanwhile, Finson is autographing pictures of himself to the students, and Sissi tells him she wants to be in his latest film. He denies her request, and then Ulrich goes up to him, asking for a photo, and informs Finson he knows the Factory inside and out. Ulrich and Finson go on a scouting trip to the Factory, where Ulrich tells him that the place has a danger of falling apart, is infested with mice, has radioactive Uranium stored somewhere, and that it is haunted. The rest of the group is observing from above. Finson, however, is not scared at the least, and asks Ulrich where the elevator leads. Ulrich tells him its broken, and Finson tells the German boy he'd like him to be his technical advisor for the film, but Ulrich says the principal would never allow him to miss school.
When Finson and Ulrich return to the school, Sissi sees the chance to manipulate Ulrich to let her play a part in the movie. Herb tells her the principal would not allow it, but when Finson comes out from the Administrative Building, shocked because the headmaster would not allow Ulrich to go shoot with him, Sissi tells the director she'll tell her father to let Ulrich go if she gets a part in the film. Finson reluctantly agrees, and Sissi gloats to her allies about it. The next day, Sissi and Ulrich go to the Factory, where their cell phones are confiscated because Finson wants to connection to the outside world due to media leaks. After Sissi compares it to a desert island, Ulrich is thoroughly bothered by the fact he has to be there. Finson then shows his crew the alien, a monster he designed for the film. After Ulrich points out it is similar to the alien in Alien, Finson gets annoyed.
During the night, Ulrich sneaks out of his and Sissi's tent to go to the Lab, where he contacts Jeremie, who had been previously talking to Aelita. After Ulrich notices Sissi had followed him, the alien suddenly attacks, as it had been possessed by X.A.N.A.. Ulrich and Sissi escape to the Factory Floor. The next morning, Yumi, Jeremie, and Odd sneak past the Factory guards to try and save their friends from the extraterrestrial invader, who had tied Ulrich and Sissi up with its gooey goo shooter. Yumi rescues them with her pocketknife whilst Jeremie sends Odd to Lyoko to assist Aelita.
Meanwhile, Finson and his crew realize the alien is missing. They pursue its trail, only to be captured by its slime. The alien then chases after Ulrich, Yumi, and Sissi, who had escaped into a smaller side room on ground level. Odd gets virtualized into the Ice Sector and meets up with Aelita before they make their way to the tower. They are attacked by Hornets, however, and begin a long run towards the activated Tower. When they arrive, however, there are two Towers, and Aelita must chose one of them. In the real world, Ulrich and Yumi are being choked by the alien whilst Sissi sits crying from shock. In Lyoko, Aelita choses a Tower, then discovers it is the wrong one. Jeremie seemingly resigns in the Lab, and Ulrich and Yumi continue to be choked.
But suddenly, the Tower deactivates, and Jeremie gratefully activates a Return to the Past. It brings them back to the part where Finson is signing autographs. Instead of suggesting to give a tour of the Factory, Ulrich this time tells Finson that another alien movie had been filmed at the Factory some time ago. Angered, Finson calls his producer, and tells him to pull out. The episode ends with Finson yelling at his subordinate, who claims there was no motion picture made previously at the site.
- The original French name for this episode is Clap de fin.
- When possessed by X.A.N.A., the Alien prop strongly resembles the alien from Alien vs Predator.
- This episode was released in book form, but only in French.
- When the first wave of Hornets approaches a fleeting Odd and Aelita, the rate at which the Hornets are firing and the focus of the fire means that it was statistically impossible for both Odd and Aelita to go unscathed the first go-around.
- This episode takes place in daytime, preferably an afternoon setting. However, after Jeremie initiates the return to the past at the end of the episode, the scenes are still in a daytime setting on Earth, but outside of the Factory, it is suddenly nighttime when the Return to the Past bubble is shown.