The book is set in an alternate canon to Code Lyoko Evolution, as the events of the story and its sequels directly contrast with the latter's plot.
Jeremy and his friends accidentally find themselves plunged into a virtual world named Lyoko. During their journey, the four friends meet Aelita, a young amnesiac elf whose past is mysteriously linked to the virtual world of Lyoko and the endless secrets and mysteries it holds.
- Chapter 1: A Butterfly at the Bottom of the Sea
- Chapter 2: The Empty House
- Chapter 3: Erik Mc Kinsky
- Chapter 4: The Underground Castle
- Chapter 5: Maya's Sleep
- Chapter 6: I Am Not Human!
- Chapter 7: John F. Bullenberg
- Chapter 8: Chocolate, Books and Secret Passages
- Chapter 9: Eva Skinner
- Chapter 10: The Secrets of the Hermitage
- Chapter 11: Eva Skinner
- Chapter 12: The Mystery of the Builders
- Chapter 13: Eva Skinner
- Chapter 14: An Unexpected Journey
- Chapter 15: Eva Skinner
- Chapter 16: A Brush with the Law
- Chapter 17: Something in the Mind
- Chapter 18: The Secret Room
- Chapter 19: Eva Skinner
- Chapter 20: The First Day of School
While searching for machine pieces for his robots, twelve-year-old Jeremie Belpois and student at Kadic Academy, discovers a secret passage that goes from the park of the school grounds to a factory not far away. The manhole cover that hides the passage, the entrance to the factory and the maze-like path through the sewers is defaced in several places with a logo featuring the name "Green Phoenix".
Nonetheless, deciding to explore this new place no matter the risk, Jeremie goes. Activating the lift out of curiosity, he descends into the dark depths and discovers a room containing a seemingly ultra-sophisticated computer terminal. Dubious, Jeremie wonders if he has discovered an abandoned film set or a military project. Recklessly he stays and explores. The terminal was inactive and not linked to any hardware worthy of being called as such, he decides to search the site, certain there is another room.
The lift doesn't seem to take him anywhere else. He then discovers, while exploring the floor, a conduit that leads further down, concealed beneath a slab on the first floor. Removing it, it leads into a second room which only contains three large tubes connected to the supercomputer above, but also just as inactive. Going even further, he arrives at the end of the tunnel but is stuck by a security door requiring a pass code. Only one hint is given by the device: D3L3ND4. The word consists of 7 letters but the response can have up to 8 according to the case. Jeremie finds himself stumped on this insignia.
Jeremie returns to the school. Reflecting on his relentless headache, he overhears a conversation between the principal and Paul, a friend who is visibly the head of an cinematography club. Jeremie requests his help with the enigma. Paul doesn't waste time in solving it: it's "leet" code, a secret code which replaces certain letters with numbers. The hint word D3L3ND4 therefore really means DELENDA. It's a Latin word meaning "that which must be destroyed". This same work is recorded in the history books thanks to a speech from a Roman senator whose words have been remembered through the ages: "Carthago delenda est" which means "Carthage must be destroyed".
Back at the factory that evening, Jeremie tries to write the word CARTHAGO in "leet" code: C4RTH4G0. The doors then open on a room containing a deactivated Supercomputer. Jeremie turns it back on. He goes back up to the terminal room. A holomap activates, representing a virtual world complete with five sectors. The screens bring Jeremie into contact with a young elf-like girl.
Immediately falling for her, Jeremy speaks with her. He then realizes, stupefied, that she seems to be inside the virtual world. Since she has no memories anymore, Jeremie names her Maya. At first he thinks that she's a very evolved form of artificial intelligence. However, a Turing test and numerous discussions with her convince Jeremie of Aelita's humanity. But how the heck did she get into the virtual world?
Jeremie then studies the three large tubes on the lower floor. These cabin-like things have a strange inscription: "Scanner. Virtualisation chamber. Danger." Could it be the key to solving the mystery?
As he returns to the school to satisfy his obligations as a student, strange phenomenons start occurring around him. Firstly, he's electric shocked by a coffee machine at the school. Several days later during the evening, the robots he built turn against and attack him.
Both times, he's saved when one of his classmates interrupts: Ulrich. Seeing him bear witness to the curious happenings surrounding Jeremie, he decides to take Ulrich to the factory the next day. After presenting him to Aelita and his hypothesis as to the scanners being the gateway to the virtual world, he asks him if he'll act as a guinea-pig. Ulrich isn't very thrilled about the idea and proposes a second option.
He decides to capture Kiwi, a dog belonging to his new roommate, hidden in their room. Taking advantage of the late hours and the dog's master being asleep, he steals the dog and places him in a scanner. But Odd was woken by the kidnapping of his pet. He follows Ulrich to the factory and accidentally takes his dog's place in a scanner.
After Jeremie launched the virtualization, Odd landed in Maya's virtual world, with the appearance of a virtual humanoid cat. In this world, his natural abilities are multiplied ten times, equipped with his very own unique weapon, and superpower.
What comes next escalates to phenomenal proportions. A battle breaks out in the virtual world. Digital cockroaches take after Odd, who is forced to flee. Ulrich joins him via virtualization, in the appearance of a virtual samurai. Together, they confront the cockroaches. Ulrich with katana swinging, Odd with laser arrows blazing.
At the same time, Maya is also on the run. A number of memories then come back to her. Her real name is revealed to be Aelita. The person controlling the monsters is X.A.N.A., a program in the Supercomputer that detests the entire world and Aelita in particular, who is the Savior of this virtual world named Lyoko. Finally, she remembers the numerous towers that are spread around Lyoko are access bridges to the real world. They allow X.A.N.A. and Aelita to act on the electrical networks there. When X.A.N.A. attacks, it enters a tower and takes control. Aelita then enters the tower in which X.A.N.A. is attacking: it is radiating red glow rather than blue. Aelita enters the tower and mechanically enters the Code on an interface: X.A.N.A. is chased from the tower and the cockroaches disappear.
Jeremie then brings Ulrich back from Lyoko. For Odd, he was already forcefully brought back to the scanner after the Kankrelats shot him with lasers and took all his virtual avatar's life points away. Unfortunately, Jeremie doesn't manage to materialize Aelita in the scanners.
He then sets to work on this thorny problem. He discovers that Aelita was indeed sent to Lyoko via the scanners. But he can't bring her back because the data concerning her were modified after she was virtualised. She had obviously had memories added, probably those concerning her role in the virtual world. This cluster of memory was blocking the memories of her life on Earth.
Several days later, a new girl joins the adventure. Yumi, a year older than Odd, Ulrich and Jeremie. She discovers the factory by following Ulrich. Knowing how to fight and being able to lend her feminine ear during Aelita's time of discomfort, she is finally accepted into the group. Her first virtualization has her end up as a sort of virtual geisha, capable of fishing with two sharp fans and telekinetic abilities
Immediately after that, X.A.N.A. sends an immense virtual Tarantula. It captures Aelita and tries to drain her memory through a tube but Yumi destroys it.
Aelita is then curt, she asks Jeremie to destroy the surplus memories in order to make her materialization into reality possible. The day comes, Yumi stays on Lyoko to reassure Aelita. Jeremie does as he's told and the materialization works: Aelita exits the scanners with red hair and completely out-of-date fashion. Ulrich and Odd welcome her to Earth and bring her up to the computer room where she jumps into Jeremie's arms.
Unfortunately, when the group think they'll be able to shut the Supercomputer down and deactivate X.A.N.A., the unthinkable occurs: the extinction of the machine makes Aelita lose consciousness. Jeremie realizes that the link between X.A.N.A. and Aelita renders turning the machine off impossible.
Jeremie can't find a solution to this problem. That's when the answer came to him one day as he was sitting alone in front of his computer screen. Franz Hopper, Aelita's father and the creator of Lyoko, presented himself to him. Communicating with Jeremie, he asked him to head to the factory to "destroy X.A.N.A.!" Not wasting a second, they headed to the factory and plunged into Lyoko. At the edge of the Ice Sector, hidden behind a waterfall, they find the entrance to Sector 5: the Core of Lyoko which takes the appearance of a vast digital city composed of blue blocks. Franz was waiting for them in the form of a luminescent sphere. He then explained his plan to Aelita, they had to go to the Fifth Sector to launch a program which would annihilate X.A.N.A..
The situation then started to spiral out of control: Yumi was devirtualised by X.A.N.A.'s monsters. Back on Earth, she stumbled upon a disaster scene in the computer room: William Dunbar attacked Jeremie, under X.A.N.A.'s control. Yumi lead him into the factory to fight him away from Jeremie.
On Lyoko, on one side X.A.N.A. sent its most powerful monster: a Kolossus several meters in height that Ulrich decides to confront. On their end, Odd, Aelita and Hopper go into Sector 5 and install the program to kill X.A.N.A. on the Supercomputer.
Odd is de-virtualized by the hundreds of flying Mantas guarding Sector 5. Back on Earth, he saves Yumi just in time by catching her after William throws her off the second floor of the factory. Ulrich holds the Kolossus back valiantly but ends up being squashed.
As for the X.A.N.A. annihilation program, it requires energy to be launched from the Supercomputer. And this energy is none other than Franz Hopper himself, in virtual form. It's then that Aelita assists, in despair, with the disappearance of her father, who is sucked away by the Supercomputer and disappears forever. From there, the program launches and X.A.N.A. is removed from the virtual world while on Earth William Dunbar is freed from its grip and falls unconscious. X.A.N.A. is neutralized and the fight is over…or is it?
Tuesday the 21st of December, between the United States and Japan, the undersea cable that transmits the Internet exchanges between the two countries is malfunctioning, and before the repair robot even grazes the surface, it's back in working order with an unusual crackling noise.
At the same moment, at Kadic Academy, Aelita, Jeremie and Odd are talking about the upcoming holidays and about the "diabolical plan" they'd concocted. Right in the middle of the discussion, Aelita suddenly loses her memory and no longer recognises her friends.
The friends meet up on the 9th of January. Their diabolical plan has been put in motion: Jeremie had simply told the 5 friends of the group to meet up a day before class started at the old abandoned villa called the Hermitage, the old residence of Aelita and her father. To do this, each of them had told their parents they'd be staying over at someone else's house.
The group then found themselves reunited: Aelita and Jeremie spent the holidays together and she started to recover her memory, partially. She still didn't have any trace of a memory of X.A.N.A. or Lyoko.
While the mood is warm in the Hermitage with meals cooked by Odd and Jeremie, followed by a snowball fight in the garden, Jeremie reminds them of their reason for being at the Hermitage: investigating its mysteries. On that note, Jeremie takes out a digital camera and with his friends, they start to recount their secret adventure as Lyoko Warriors in a kind of diary. They especially hope that this will help Aelita to recover her memory. Ulrich firstly recounts their unusual encounter with Jeremie.
At that same moment, elsewhere, a young American fan of the Ceb Digitals group and their singer Gardenia receives an email from a supposed member of a forum. The email seemingly contains a photo of the artist from the band. When he opens it, he realises that it's just a fake.
The only image that opens on the boy's computer is a logo. A very familiar eye. In Erik's computer, rummaging about, X.A.N.A. prowls, brought back to life and without memory, it searches for its own memories throughout the Web.
While Jeremie recounts the entirety of his exploration of the factory, his discovery of the Supercomputer and his meeting Aelita, whom he originally named Maya, X.A.N.A. enters a large music site from which the owner can't chase it out, then leaves and passes through the mobile phone network, still searching for the memories it no longer has.
Interrupting their diary for a moment, they escape the cold in the Hermitage. Yumi showers to get warm while Odd and Ulrich watch a horror film. Jeremie and Aelita talk about Lyoko and X.A.N.A. in the kitchen, while preparing hot chocolate. Following her friends' story, some memories from her virtual life came back to her. After Odd kindly slipped some peppers into Ulrich's hot chocolate, Yumi proposes they explore the Hermitage's attic. While they return to the mess in search of a clue, Aelita asks why the Hermitage was abandoned. The students then tell her the start of the story, which they hadn't already addressed. They remind Aelita that her father was Franz Hopper, a very smart man who created the Supercomputer and Lyoko. They also tell her that before she was virtualised, she was already a student at Kadic Academy, but everything changed for an unknown reason on June 6 1994 when her father fled with and virtualised her urgently. Aelita then asks about any news about her mother, but on this too, they have absolutely no information.
Odd then proposes a game of hide-and-seek to loosen the atmosphere. Jeremie takes advantage of it to take Aelita down to the Hermitage's basement and find out a little more about her father. He reveals to her that the old villa possesses a number of secret passages, a number of which are still unexplored and some of which lead to the factory. No complete plan of the house seems to have been left by the people who came after Hopper fled. Aelita then realises that the Hermitage must have been built by someone. And that's when at the back of a dead end, she and Jeremie find a sack of cement labelled with the proprietor: "Broulet and Brothers", a masonry company at 117 Rue de Trivoli, at the other side of the city.
Outside, Ulrich and Yumi are looking for a place to hide in the garden. When William, another boy in from their school passes not far from the Hermitage, Ulrich tackles Yumi to the ground so they won't be seen. Taking his reaction as one of jealousy, Yumi becomes angry and scolds Ulrich, who is left speechless.
Meanwhile in the United States, Eva Skinner, a young, trendy girl who's president of the Ceb Digital's local fan club is preparing to help out at one of their concerts at her school. When she touches her computer, the Eye of X.A.N.A. appears on it and a spark jumps from the mouse, remaining in her all the way until the concert and the moment when she begins to feel ill. Waking up at a hospital, Eva Skinner's body fights weakly for a moment against X.A.N.A.'s grip, which had taken over her body. Eva ends up being completely overwhelmed. X.A.N.A., strong with a newly-acquired body, escapes the hospital through a window and steals the clothing of a passer-by before going by its new identity: Eva Skinner. Collected by a police officer, she asks directions how to get to France. Once informed, she gets rid of the officer, takes his car and departs for San Francisco airport (Chapters 9, 11, 13 and 15).
In France, leaving Ulrich and Yumi at the Hermitage to reconcile in Aelita's company, Odd and Jeremie go to the address they discovered. Invited to have tea with the owner of the building, they learn that the Broulet brothers' company is no more. After the death of two of the three brothers following a scaffolding accident, the final brother sold shop and moved out. The visit is nevertheless a success: Jeremie and Odd return with the phone number of the third Broulet brother, Philippe Broulet.
Back at the Hermitage, Jeremie calls the man. The tentative call from Jeremie turns up short: the moment when he mentions the name Hopper, Philippe declares he knows nothing and hangs up. After a short debate, the group then decide to go to Provence, straight to their contact's house, because one thing is obvious: he knows something. Jeremie reserves train tickets by hacking Kadic's accounts and paying with the principal's credit card. Go there in the afternoon, return that night.
Quickly disembarking from the TGV at Marseille-Saint-Charles station, the heroes arrive at the house of Broulet's son and his wife. After some negotiation, they end up talking to Philippe Broulet.
After some long hesitation, the man comes to the table and reveals to them why he didn't want to talk to them about that time in his life. At that time, a mysterious individual contacted him and asked him and his brothers to do a large amount of work on an abandoned factory. Philippe Broulet understood that the work was probably a government secret: they were driven to the site blindfolded, the group that sent them payments via bank deposits didn't exist: it was a shell company. But the colossal amounts of money they were paying encouraged them not to ask any questions.
Later, the same mysterious man accompanied by Franz Hopper had them build the Hermitage under the same circumstances. In the end, the final part of the story occurred when Franz Hopper, exhausted and visibly worn by his work, asked him for a final service: build a room in the Hermitage and make it completely concealed from the outside. During this period, Franz was no longer accompanied by the mysterious individual. He was nervous and very stressed. He paid Broulet generously, though much less than previous times.
The final story won the group's attention: Franz walled this room up to protect it. He had to deal with the fact that it could appear on a plan of the house and he had left a map that "only the right person can find."
Leaving the Broulet house, they rush to the train a little before 11 o'clock to have the time to check the Hermitage the next day to search for this mysterious room, before school comes back. In their hurry they take the train before the one they booked without having changed their ticket.
The troubled then begin for them. They come across a psycho and slightly schizophrenic transit officer. He, not content with just checking their tickets, questions how they were able to pay: the principal's credit card. Not believing the group's lies for a second, the officer refuses to allow the unaccompanied minors to stay on the train and hands them over to a police officer at Lyon.
Agent Crane is luckily far more understanding than the transit officer. They admit their mistake in hacking the principal's credit card. When Aelita tells him why they made their trip: to find information on her deceased father, the agent is touched and accepts to not alert their parents. He let them off with a warning and forces them to reimburse the principal's account electronically, then arranging with his brother to take the kids back to Paris on a truck in the night. The trip is uncomfortable but the group are saved from a good scolding from their parents.
Back in the Parisian region, the group get to the Hermitage. Reflecting intensely, Aelita ends up finding the message her father left for her. It was hidden in invisible ink in a seemingly empty notepad Aelita found at the Hermitage. To reveal the ink, they needed to use a chemical ingredient contained in a chemistry set, hidden in the attic. Hopper betted on his daughter's passion for chemistry to hide the message where only she could find it.
Thanks to the instructions in the notebook, the group find the secret room in the Hermitage. Hopper left an old video cassette there, and what a show it was. It contained old family photos of Aelita, notably photos of her mother, Anthea.
In the recording, Franz then explained why things happened. Franz Hopper's real name was Waldo Schaeffer. He and Anthea worked together for a long time on a revolutionary project in Switzerland, Project Carthage. Realising that the project wasn't destined to save humanity but was a risk, a road to ruin, they left the project. Anthea was captured at that time. Franz then built his Supercomputer and Lyoko, using the same programs they developed for Carthage. The goal was to protect people from Carthage itself.
Things then went bad when the men of the project found Hopper. In the escape, Aelita was gravely injured in the head. Hopper had no choice but to virtualise her to save her, despite the danger X.A.N.A. represented.
Hopper leaves his daughter two missions at the end of the video. For one, shut the Supercomputer and X.A.N.A. down so humanity can never use them for evil means. Then, find Anthea, who is still alive but in the hands of Project Carthage. Unfortunately, some interference cuts off some of the goals he sets in the video, and the cassette doesn't reveal the end of the message because of its obsolescence.
The next day, the 10th of January, the group arrive at Kadic for their first day back at school, ready to begin once again their double lives and go on the search for Anthea.
At the same moment, Eva Skinner takes the plane from San Francisco to France. Hacking the Kadic files, she was already enrolled as a new student and had time to reflect on her plan to approach the Lyoko Warriors, develop a friendship with them, and annihilate them once and for all for her master.
Differences from the Show
- The group's adventures on Lyoko are drastically abridged, with only four specific trips being mentioned. The first features the group meeting Aelita, similarly to X.A.N.A. Awakens. The second features Yumi's first trip to Lyoko. The third focuses on materializing Aelita to Earth, similar to Code Earth. The fourth and final adventures sees the group meeting Franz Hopper on Lyoko, journeying to the newly-discovered Sector Five, battling the Kolossus, and using all of Hopper's energy to initiate the program to destroy X.A.N.A.; essentially the episode Fight to the Finish. In addition, all of the missions play out very differently from how they were portrayed in the show.
- Turning on the supercomputer is far more difficult in this version of the story; Jeremie is forced to break multiple codes in order to get it powered up.
- The factory is dimly lit, requiring a flashlight in order to be explored, and the sewer tunnel is still in use.
- Aelita's link to the supercomputer is not due to her stolen memories, but due to an excess of data in her mind. Jeremie is forced to delete it in order to materialize her to Earth.
- Also, apparently any monster can steal Aelita's memories, provided they make physical contact.
- Yumi joins the group after Ulrich 'accidently' tells her about the supercomputer, prompting her interest.
- William only plays a part in the story during the final mission, where he is possessed by X.A.N.A. on Earth.
- The return to the past feature is never seen or mentioned.
- The Subdigitals are called the 'Ceb Digitals.'
- Aelita has a thick scar under her hair; the result of a bullet wound she received while escaping Project Carthage. It is implied her time in Lyoko is what healed her.
- Odd's mother is apparently not as supportive as she is in the show; according to him, she frequently predicts he will end up in prison one day.
- Aelita has red hair in the real word unlike in the television series where her hair is pink.
The book was never published in English. The title shown is a translation.
- In Italian, the book was published as "Il castello sotterraneo"
- In French, the book was published as "Le château souterrain"
- In Spanish, "El castillo subterráneo"
- In Catalan, "El castell subterrani"
- In Galician, "O castelo subterráneo"
- In Basque, "Lurpeko Gaztelua"
- In Portuguese, "O castelo subterrâneo"
- In Dutch, "Het Ondergrondse Kasteel"