In Jeremie's dorm room, he, Aelita, Ulrich, and Yumi relax before going to class. Suddenly, Odd arrives and warns them of a surprise dorm inspection being conducted in just a few minutes. Fearing Kiwi will be discovered, Odd asks Yumi to take the dog to her house for the day. Despite her father's aversion to pets, Yumi reluctantly agrees, and takes Kiwi to her house, where she asks Hiroki to watch him before returning to campus and going to class.
After morning classes let out, Odd, Ulrich, Jeremie, and Aelita meet with Yumi in the courtyard, where Odd is expresses a lack of confidence in Hiroki's ability to properly care for Kiwi, whom he calls "very sensitive." Jeremie's laptop then beeps, and he announces to the others that the Superscan has detected another Replika. All five Lyoko Warriors arrange to skip their afternoon classes and meet at the Factory, where Aelita, Yumi, Ulrich, and Odd are sent to Lyoko.
After boarding the Skid, Aelita pilots the ship to the new Replika, which is revealed to be a copy of Carthage. After mooring the Skid to a tower in the Core Zone, Jeremie activates the tower and uses it to translate Odd and Yumi to the supercomputer generating the Replika. When they arrive at their destination, it is then revealed that the supercomputer hosting the Replika is aboard a new international space station orbiting 400 kilometers above the Earth.
As Yumi and Odd float through the station, they find X.A.N.A. is manufacturing small metallic orbs of unknown use and function. Meanwhile, on the Replika, a trap is suddenly activated, and a red halo appears over the Skid, causing continual damage to its shields. Jeremie discovers the halo may be destroyed by triggering a Key Mechanism like in the original Carthage, and Ulrich, who has been guarding the Skid with Aelita, begins exploring the Replika, searching for the Key. On the space station, Yumi and Odd find the supercomputer, and Jeremie encourages them to make its destruction look like an accident in order to avoid any accusations of sabotage among world governments.
As Ulrich maneuvers through various obstacles including a Creeper in order to reach the Key, Yumi and Odd are attacked by the metallic orbs, which are revealed to be complex weapons capable of flying, sprouting spikes, and generating enough heat to melt the station's metal doors. While Odd and Yumi retreat from the orbs, William arrives on the Replika and begins damaging the Skid even further, forcing Aelita, who has reentered the Skid in order to monitor its shields, to disembark and intercept him. When the orbs advance on Odd and Yumi, Odd opens an emergency hatch, sucking the orbs and several supply boxes out of the space station.
As Aelita faces off with William, Ulrich finds and succeeds in triggering the Key Mechanism, destroying the halo and saving the Skid. However, he is crushed by a lowering ceiling and devirtualized in the process. Meanwhile, on the space station, Odd and Yumi return to the supercomputer and use a hammer they find on board to burst a water pipe, short circuiting the supercomputer and causing it to explode. Jeremie then sends Yumi and Odd back to the Replika, where they help Aelita battle William. Upon finding himself outnumbered, William simply retreats, and Aelita, Odd, and Yumi board the Skid and exit the Replika as it disintegrates.
After returning to Earth, Yumi and Odd head over to the Ishiyama house together, where Yumi discovers her parents are home from work, and worries over what they will say about Kiwi. However, it is then revealed that Mr. and Mrs. Ishiyama have taken a liking to Kiwi despite Yumi's assumptions, and even ask Odd if they may keep him for a week. However, when Odd refuses, Mrs. Ishiyama gives him a box of homemade sushi to feed to Kiwi.
- The original French title for this episode is Planète bleue, which translates to Blue Planet in English; this is a nickname for planet Earth.
- This episode's English name is a reference to a 1969 song of the same name by David Bowie. It may also be a reference to the 1968 Stanley Kubrick film 2001: A Space Odyssey, or the 1968 Arthur C. Clarke novel of the same name.
- Despite the Lyoko Warriors clearly going to classes in this episode, Hiroki, who attends the same school, appears to stay home to watch Kiwi. It is unknown why Hiroki is not in school during this episode.
- This episode marks the only time in the series where the Lyoko Warriors find and destroy a Replika in the same episode.
- This episode also marks the only appearance of X.A.N.A.’s spiked orbs. The orbs were a hybrid of the morning star and the mace. They featured spikes which could be expanded or retracted as needed, can propel themselves in a zero-gravity environment, and heat themselves up enough to burn through solid metal while still working. These were vented into space.
- While Odd and Yumi are in the room with the space station's supercomputer, the pink marks on Odd's face are missing in one shot.
- Near the end of the episode, Jeremie removes his earpiece and places it on the keyboard. However, in the very next shot, he still has the earpiece in his ear.
The original episode summary can be found here.