Exploration is the third episode of Season 2 and the twenty-ninth episode of Code Lyoko.

Plot

The Lyoko Warriors, especially Ulrich, are starting to get a little tired of trips to Lyoko and X.A.N.A.'s constant assaults. However, they are aware that there will be no progress made until an anti-virus can be found to separate Aelita from X.A.N.A.. Aelita suggests an exploratory trip to the newly discovered Sector Five, thinking it may hold information on finding the anti-virus. Jeremie refuses, stating that it is still unexplored. Odd points out that Sector Five is full of "ultra-dangerous traps", powerful monsters, and the Scyphozoa, which wants to try and steal Aelita's memory. After a long talk, they decide to set out for the new sector tomorrow.

However, Yumi is forced to withdraw herself from this expedition since her constant late-night trips to Lyoko have been noticed by her parents, resulting in them losing their trust in her. Under advice from Jeremie, she reluctantly agrees to stay away from Lyoko for a little while until she can get them to trust her again. 

The exploration goes on ahead without Yumi. Jeremie sends Odd, Ulrich, and Aelita into the Forest Sector, where he types in the Scipio code in order to make the Transport Orb to appear. Sector Five turns out to be more complicated than the group envisaged; with a countdown which, if not stopped, will change the structure of a room. Aelita, Odd, and Ulrich try to escape the Core Zone but only find themselves lost in a maze. While trying to find their way out, Aelita loses 40 Life Points at the hands of X.A.N.A.'s new monster: the Creepers. When they see the light at the end of the room, they wind up in the Celestial Dome. Jeremie then finds a mechanism, which he believes could stop the countdown. Unfortunately, Odd and Ulrich are devirtualized before the countdown ends and Aelita finds herself trapped as the structure of the room changes. Jeremie soon horrifically discovers that Ulrich and Odd have not been materialized on Earth and are now stuck in limbo. Jeremie and Aelita find themselves in a crisis situation not knowing how to find the data for materialization from Sector Five. Aelita wonders if Jeremie will be able to find the right data codes but he in despair tells her that it's "probably as easy as looking for her anti-virus".

At home, Yumi is enjoying a peaceful night with her family, playing a game of Go, until she gets a call from Jeremie. She manages to leave the room and call Jeremie back, who explains the entire situation to her, forcing her to go to the Factory to help. 

Unfortunately, Yumi's absence has not gone unnoticed when her mother goes into her room to talk with her, only to find her gone and the window left open. Having had enough, Yumi's parents inform the principal and Jim, who assure them that Yumi is likely just on the campus with the rest of her friends. However, it is discovered that the rest of the group is also missing from their rooms and, thanks to Sissi, who arrives on the scene, come across Kiwi, who is hidden inside Odd's room. Using the dog's nose and Odd's smelly sock, the search party heads straight for the Factory.

Things don't look good for Aelita as the Scyphozoa arrives to steal her memory. Yumi is virtualized onto the Mountain Sector, where she dashes to get to the edge of the sector. She's suddenly attacked by two Kankrelats, but luckily, she arrives in Sector Five just in time to deactivate the countdown and free Aelita from the jellyfish, getting the two of them to an outer area of the sector. The girls see how Sector Five looks from the outside and Yumi notices the Interface at the end of the platform. Aelita decides to log in and she's amazed by the fact that she can access X.A.N.A.'s data and tells Jeremie and Yumi and X.A.N.A. lives in Sector Five. Jeremie asks her to look for a devirtualization codes from Sector Five to bring Odd and Ulrich back to Earth. However, the duo encounter several of X.A.N.A.'s Mantas, and Jeremie sends them Overwing when Aelita is done with searching. They fly around the Celestial Dome and see four tunnels and Jeremie quickly deduces that they must correspond to the ones that open onto the arena and manages to open one of them. Just before flying into it, Yumi eventually is shot off by a Manta and devirtualized. Aelita then leaves Sector Five through the open tunnel and arrives in a way tower in the Mountain Sector before finding inactive tower so Jeremie can use Code: Earth devirtualize her. Thanks to the interface discovered by Aelita, a program is retrieved to re-materialize Odd, Ulrich, and Yumi, and the group is reunited once again.

However, there is a surprise waiting for the heroes as they leave the Factory: Yumi's parents, Principal Delmas, Jim, and Kiwi who are all waiting for them. Jeremie, realizing what needs to be done, escapes back to the Supercomputer. Jim manages to get onto the elevator as well and is shocked upon seeing the Supercomputer, even though Jeremie tells him he's been there before, confusing him. Jeremie launches a return to the past and, finally, everything is back to normal.

Back in front of the school, Yumi's parents still want to know what she's been up to, so she tells them an excuse that causes them to decide to leave her alone; she's "in love." However, what it is she told them will forever remain a mystery to her friends, who know only that what she said is "the truth" upon asking her about it. 

Trivia

• The original French name for this episode is the same as the English.
• From this episode onward, Jeremie's cutscene spells his name as "Jeremy".
• This episode shares several similarities with the Evolution episode, Cortex:
  • A new area explored.
  • Traps kill each of the Lyoko Warriors one by one.
  • To materialize Lyoko Warriors, a terminal must be accessed.
  • Aelita is left alone (everyone else on the mission was gone).
  • Someone is sent to the rescue (Yumi/William).
  • Aelita gets to the terminal and gets the program to materialize everyone.
• This episode marks the only time where Yumi openly declares her romantic feelings for Ulrich, as opposed to just blushing or other cryptic hints.
• At the beginning of the episode, Odd seems to break the "Fourth Wall" when he says "You missed an episode, Ulrich.", when Ulrich stated that he wants to be done with X.A.N.A.
• When Yumi is at her house, before being contacted by Jeremie, she is playing Go, a strategy game that originated in China, with her father.
• This episode marks the first appearance of Hiroki Ishiyama and the Mantas.
• This is the only episode to feature a laser field trap in Sector Five.
• This is the first episode where a return to the past was launched after a mission but no tower was activated.

Errors

• When Kiwi was at the park and going around the sewer's tunnel it was closed, but Jim just got there without doing anything.
• When Yumi tripped the key it was gone, but after the walls were open and Yumi leaves, the key appeared to not be tripped.
• At one point in this episode, Jeremie's collar disappeared.

Gallery

Aelita and Yumi stand in the Celestial Dome.

Yumi tries to quietly sneak back inside her home…

... but is soon caught by her parents

Yumi sleeping.

Her parents walk her to school the next day…

Ulrich, Odd, and Aelita ride their vehicles through the Forest Sector.

Odd doesn't feel too well after they've been dropped off by the Transport Orb.

They explore Sector Five.

Jeremie warns the group of the count-down and it's key.

Odd spies the key high up on the Sector wall.

Ulrich is devirtualized by a lone Creeper.

Aelita trapped in Sector Five alone.

Jeremie trying to figure out a way to bring Odd and Ulrich back.

The count-down reaches zero!

But Yumi activates the key just in time.

Aelita and Yumi ride the Sector's elevator.

Jeremie and Aelita wait for their friends to arrive back into the real world…

The group head into the Factory elevator, exhausted from their battles.

"Return to the past now!"

Ulrich is virtualized onto Lyoko.

Yumi playing a game with her father.

Discovering the chamber for the elevator, which will not come until the key is tripped.

Odd, Ulrich, and Aelita find another area in Sector Five.

Yumi about to be picked up by the Transporter in the Mountain Sector.