After reading about a dead man named Leon Corbe, who died during the construction of Kadic, Sissi decides to hold a séance to communicate with him. She manages to convince Ulrich to attend. During the séance, one of Xana's ghosts appears in the form of a four-armed monster. At first, it seem docile, but quickly gets angry and attacks. Ulrich leaves Sissi with Odd while he goes to tell Jeremie. Jeremie can't find an activated tower, which seems wrong considering the situation. As Jim patrols the hallways, he is picked up by an invisible object. Jeremie, Odd, and Ulrich arrive to spray it with a fire extinguisher, confirming that it's a ghost and implying that the super scan is broken. With the ghost on the loose, the group heads off to the factory. After they arrive, Aelita, Odd, and Yumi head to Lyoko. Odd looks for the tower while the other two head to The Carthage Region to fix the super scan. Meanwhile, Jeremie and Ulrich are left to deal with the ghost.
During the school physicals, Xana possesses the school nurse, Yolande, and has her kidnap Aelita. The rest of the group beats her to the factory, but has no way to get Aelita from the far more powerful nurse. Having no other choice, Jeremie decides to test out an experiment which will give a person the same powers as one possessed by Xana. To do this, he has to activate a tower like Xana. Jeremie's towers turn green instead of red. Odd volunteers, and is enhanced by a ghost of Jeremie's design. This allows Odd to fight the nurse effectively while the others deactivate the tower. This fortune doesn't last, however. Xana is able to take over Jeremie's tower, reversing the effect of the ghost to drain Odd's energy. And on Lyoko, Xana makes everything invisible. Now the group has to deactivate not only the original tower, but the tower that's draining Odd's energy.
The contestants have to draw inspiration from their surroundings while outside in New York. The designers have a budget of $100 and one day to complete the outfit.
When both his job and arcade skills seem to no longer impress Dominic, Jimmy hopes getting entry into The Guinness Book of World Records will again make him cool in his son's eyes.
Russel knowing that Larkin and their unborn child's life is on the line he must stop Larkin from reporting what she knows. Sheriff Underlay is shot and drifts between the past and present.
Captain Hero's x-ray vision makes a housemate ill. Distraught, he seeks to give up his super powers.
J.D., Turk, Elliot and Carla are interrogated about the mysterious death of a patient. Dr. Kelso learns, that J.D. and Turk were away tracking down a patient, Elliot was traumatized over finding out that her make-out buddy was married and Carla was busy recruiting hospital personnel for a group lottery purchase.
In a "Wizard of Oz" homage, J.D. is trying to go home, Turk searches for a heart donor and Carla worries, that she doesn't have the courage to become a parent. Meanwhile, Elliot doesn't believe, that she has the brains to lead a question and answer session. Also, the Janitor is painting color coded lines throughout the hospital for easier navigation.
A new TV show turns everyone in Retroville into mindless and exceedingly cheerful zombies.
When Carol discovers her best friend Lillian had an affair with her husband back in the seventies, she takes revenge by reporting her to the DSS for benefit fraud. Frank Gallagher, who has been posing as Lillian's dead husband and claiming his benefits, comes under suspicion.
Mac and Templeton head out west to pay tribute to the dedication of former President Bridges' Presidential Library. While there Air Force One is held hostage by a guy who wants to speak with Mac. Meanwhile Horace and Rebecca have some friends for a party.
Ruby and Gracie want to get their ears pierced but Cheryl believes that this will lead to the girls growing up too quickly and convinces Jim. Jim and Cheryl renew their wedding vows and Jim walks down the aisle with an earring.
Alan and Denise take on the case of a young girl whose father killed her mother after finding the mother's whereabouts through her HMO's website. Catherine Piper comes back into Alan's life - by robbing convenience stores. Beverly Bridge, Denny's fiancée, flexes her muscle around the firm -- meanwhile, Brad attempts to manage the situation for Shirley and Paul. Daniel goes in for chemotherapy, and attempts to shut out Denise.
The Strike Team tries to develop a strategy to deflect the Internal Affairs investigation as Vic finally comes face to face with Kavanaugh. Meanwhile, Tina goes undercover to help take down a sex-trafficking ring; and friction between Claudette and Dutch deepens when she reopens one of their past cases.
The NCIS team investigates the murder of two Marine wives, and must find the murderers before they attack their next target, another woman.
Jack returns to CTU and has an emotional reunion with Audrey, while Curtis tracks the Russians and the stolen nerve gas. Walt sends in a hit man to silence Jack. Chloe discovers that Spencer has his own agenda at CTU. Walt convinces Logan to have Martha institutionalized when she tells them of the attack on her.
Sheppard's team meets a civilization about to be destroyed by a super-volcano, and is trapped there when the Stargate is destroyed during the evacuation.