While Chris develops a crush, Julius and Rochelle have their work cut out dealing with all of Tonya's and Drew's admirers.
Chloe is possessed by the spirit of a young girl whose body is sealed in the Talon's walls, and goes searching for the girl's killer while Clark and Lois try to track her down.
After a child's kidney tumor disappears, his father credits the cure to water from a particular spring. Hood and Rachel rush to the scene to investigate - along with a horde of hopeful cancer patients. But if the water has such curative power, why does it seem to make so many people sicker?
Kaitlin prepares herself to head back to school. Ryan has doubts about his relationship with Marissa after helping out Sadie. Kirsten and Julie make plans for a Valentine's Day party.
Earl's nervous about returning a laptop computer he stole from a college professor, mostly because he's uncomfortable around smart people. When the professor turns out to be a beautiful woman, he feels even more ill at ease, until she flatters him and asks him to speak about his list in front of her class. Meanwhile, Randy experiences fraternity life---and absolutely loves it.
The group travels to Las Vegas and plays strip poker, an infatuation develops between two contestants, and a couple is eliminated.
When Leah Robinson goes missing after a confrontation with a young man at an art gallery, the team mvoes in to investigate and soon become suspicious of Leah, suspecting her of murdering young women that she believed to be involved with her husband, Ken. Ann isn't quite ready to take her romance with Jack public, and their relationship gets rocky when their different methods of handling the case tip off the suspect.
A reality show where a group of contestants are stranded in a remote location with little more than the clothes on their back. The lone survivor of this contest takes home a million dollars.
A half-naked woman is found half buried in the desert with a branding on her arm. She has no hair and is missing her right hand. The woman turns out to be Lady Heather's estranged daughter. The autopsy reveals that the woman was a victim of an experiment and starved to death. The team investigates the Betz Clinic where the deceased underwent a sleep therapy session for her insomnia.
An unexpected visitor puts Clemente in the middle of a domestic dispute. Meanwhile, Luka and Abby await test results on their unborn child; Neela struggles with her surgical elective and Pratt ends up with an unexpected suitor when he participates in a charity bachelor auction.
Ash and co have arrived on the island of the Battle Palace, which happens to be a massive jungle. Ash, eager to make his upcoming battle with the Brain as good as it can be, decides to put extra emphasis on helping his recently evolved Sceptile to be able to use its attacks. However in the process, Ash and Sceptile get separated from the group and meet with the Frontier Brain, Spenser. Will Ash and Spenser get Sceptile to be able to use attacks again?
Red lets Hyde in on a Valentine's Day secret; Christine opens up to Jackie about her love life; and Randy has big plans for a date.
It's nearing the end of the year and Jeremie's research has hit a dead end. After the group collects some data from The Carthage Region, he plans to use a tower to decipher Franz Hopper's diary. Before the mission, Odd gets a message from a mystery girl. When he goes to meet her, he is attacked by one of Xana's ghosts and locked inside a well at the Hermitage. The ghost then assumes Odd's form and goes to Lyoko in his place. The tower that Xana activated to make the ghost then deactivates, confusing Jeremie. Putting it out of his mind, he begins his plan to decipher the diary. Shortly after they begin, the ghost turns on the group, devirtualizing Yumi and chasing Ulrich away from the tower as three Tarantulas arrive to protect it. At the same time, Xana attempts to take over Jeremie's tower, locking the decoding procedure so they can't abandon it. Jeremie realizes the true nature of the ghost during the fight, and Yumi goes off to find the real Odd. After the ghost proves to be ineffective against Ulrich, it shape-shifts into a clone of Ulrich. In this form, it proves to be an equal match for him. After much fighting, Ulrich finally beats the clone, but is taken out by a Tarantula shortly after. Just when it looks like Jeremie's tower will fall, Franz Hopper steps in and protects it. The diary then decodes fully. After examining the diary, Jeremie tells Aelita that she is Franz Hopper's daughter.
After going through all of Franz Hopper's diary, Jeremie discovers the truth behind the supercomputer, at least to some extent. Hopper had used it quite extensively, to the point of repeating a single day for more than seven years. His sanity degraded throughout the experience. Hopper also revealed that he and Aelita hold the keys to Lyoko, which Xana was after. He only needed her half, now. The keys would allow him to escape the supercomputer. Jeremie also finds a way to free Aelita from the supercomputer. It turns out that Aelita never had a virus. In fact, Xana had been holding onto a piece of her, which was responsible for linking her to the supercomputer. Aelita is not willing to go, angry over the fact that Hopper had essentially taken her life from her. She's also worried that Xana might escape. To that end, she shuts down the supercomputer. Jeremie rescues her, and the group goes to Lyoko to retrieve her fragment. After all their efforts, they seem to succeed, but it turns out to be a fake. Xana manages to devirtualize Aelita's defenders and steal her memory, effectively killing her and allowing him to escape, which shuts down Lyoko in the process. His escape allows Franz Hopper to revive Aelita and Lyoko, restoring all of Aelita's memories in the process. Through the restoration, Aelita finally remembers her past up to the point that she went to Lyoko. With Xana now free and Aelita's memories returned, neither are linked to the supercomputer. This means that they could shut it down, but it would do no good. Unsure of how they'll proceed, Jeremie promises that they'll find a way to stop Xana.
Max starts to wet the bed and George makes fun of him, but when this keeps happening, Vic thinks that Max may be sexually active. So they take Max to the doctor to find out that Max's kidney needs to be taken out.
When the profits from the Neptune High Winter Carnival go missing, Veronica finds herself defending Jackie from the condemning teachers and students. Meanwhile, Keith meets with her father, Terrence Cook, after he is accused of playing a role in the bus crash, and Logan initiates a new relationship while Beaver continues an old one.
This episode demonstrates the production processes for escalator handrails, highlighters, guitar strings and wigs, and shows how each is made.
Brooke is forced to grow up in a hurry when her trip to a New York City fashion show prevents her from attending an annual cheerleading tournament. Nathan and Lucas are influenced by the father of an old friend. Struggling with her mother's cancer, Peyton joins Rachel for a night of blowing off steam, and Haley and Nathan use their hotel room as the honeymoon suite they never had.
Brennan and Booth investigate the origins of a decomposed body that's been found in a local alley and determine it's the remains of a shy teen with an alter ego.
Some of the island survivors fear that "The Others" may have returned when Sun is greatly injured during a failed kidnapping attempt at her plant garden. Also, the trust barrier becomes very thin between Locke and Jack in terms of locking up the guns and being kept safe. Meanwhile, Sawyer is an amused but highly interested bystander when tension escalates between Jack, Locke, Kate and Ana Lucia. When Jack purposely takes Sawyer's medication from him he pushes more in favor of helping Locke. Lastly, flashbacks reveal more of Sawyer's con artist past.