In the shocking, action-packed season finale, a determined Veronica must betray someone she cares deeply about in order to solve the season-long mystery of who murdered her best friend Lilly Kane, but what she discovers puts her life in serious danger. Meanwhile, on the eve of a reception for the Governor of Calif., Jake Kane asks Duncan if he really wants to know what happened on the night Lilly died. Later, Keith awaits the results of a paternity test.
Rory is surprised by the performance review she receives from Logan's father. Luke's plan to buy the Twickham house is threatened by a competing bid.
House and his team tackle the case of a young man with a penchant for odd behavior, and House prepares for his date with Cameron.
With their residencies over, there are big changes at Sacred Heart. J.D. moves out to live on his own, while Turk and Carla consider a family change, creating another rift in their long friendship. Jordan is hired to handle some paperwork for Kelso, which annoys Cox. Elliot has a job interview at a different hospital thanks to her boyfriend Jake.
When Tony opens a mysterious letter thinking it's for him, a small puff of white powder comes out and it releases a possible deadly virus. Kate calls for help and soon she and Tony are isolated in a bio-hazard isolation room for precausion. McGee and Gibbs work to discover who sent the envelope and how to cure their friends before its too late for them. Meanwhile, Tony's health gets worse...
After a young woman's baby is tossed out of a car, Benson and Stabler investigate to find out what happened, and after learning the young woman is addicted to prescription pain killers, their investigation leads them to an elderly woman named Jenny Rogers, who lives with her son Kevin and daughter-in-law Carol. The young woman finally identifies Carol Rogers as the person who solds her the drugs, but when detectives go to confront Carol they find her body, and are left trying to uncover who really killed Carol.
When George and Angie find out that Carmen and her boyfriend, Jason, have become more intimate under their roof, they think about asking Jason to move out. But when they discovers that Jason has been using steroids provided by none other than the boy's own father (guest starring Stacy Keach), their concern for his health causes them to reconsider.
Michael sells his trucking business to spend more time with Jay and Junior Junior.
Jim receives a taste of his own medicine in a prison cell of his own... How will he get out of this situation!? On G-Wing, Governor Neil Grayling starts to make changes and announces that he will take full responsibility for the wing. Two newcomers arrive - Janine is furious with her partner-in-crime Arun for confessing to their credit card scam. Tina O'Kane hates her new freedom and tries her best to get back inside... but will she end up on G-wing or on another wing? Bev and Phyl plan to teach Bodybag a lesson. Top Dog Natalie Buxton is rubbing up her fellow inmates the wrong way.
Cheryl and Dana think they have cause to worry when Dana's fianc - wants to race fast cars and Jim wants to take up skydiving.
Jim actually remembers his and Cheryl's anniversary - but Cheryl didn't! Improvising, she gives him the photo album that covers years worth of memories. They start reminiscing.
After a near-death experience in a Jean Boutique, Grace decides to write her will and enlists Will's legal expertise to make sure she's fair when bequeathing her money. Grace visits Will's mother to find out how much Will plans to leave her and is shocked by what she finds. Thanks to Grace, Will also takes a look at his life and decides it's time to make a life altering career move. Meanwhile, Jack and Karen find an imposter teaching Jack's McFarland Method Of Acting. Realizing he needs new material to get back into teaching, Jack changes his method to win back his students.
Robert discovers Pat smoking and she pleads for him not to tell anyone. When Amy later smells smoke on Robert, she tells everyone that he has been smoking. When Pat doesn't tell the truth, Robert ends up being yelled at. The next day, he tells Ray and Debra the truth, but it doesn't take long for the two to blurt out the secret in front of everyone, which leads to many more secrets being revealed.
An angry Ephram makes a bold move - and breaks his father's heart in the process - in an attempt to raise money for a plane ticket to Europe by selling his music equipment, except his piano, to "muscian" Jared and his band. Meanwhile, Nina can't quite put her finger on why Andy has been acting strangely of late, whereas a more perceptive Delia comes right out and asks her father whether he has feelings for Nina, and Bright's green-eyed monster makes an unexpected appearance when Hannah (Sarah Drew) goes to the prom with Topher (guest-star Lukas Behnken). Hannah becomes very upset when Bright insults her dress. Bright goes apartment hunting. Lastly, Rose begins her treatment at the hospital with Harold by her side.
A former high school football star is murdered at a reunion, the CSIs must find the killer. The victim was the big man on campus in high school and there are a lot of guests at the reunion with reasons to resent him all these years. Now, the team must investigate everyone, from the head cheerleader to the school misfit, to see who held a decade-old grudge big enough to kill. Meanwhile, Horatio and Delko arrive at a crime scene and discover that it's already been processed, leading Horatio to uncover further information about his brother possibly being alive.
After Flex hurts Danielle's feelings by teasing her for being fat in high school, he tries to make it up to her by recreating the prom she never got to attend. Meanwhile, after agreeing to let Spirit design her prom dress, Breanna is furious when she shows up to the prom in the dream dress she wanted to wear.
Toni is surprisingly excited about a visit from her mother, as she hopes to be pampered before having her baby. However, she soon learns that her mother actually came to town because she recently received a letter from an ""old friend""--and is considering having an affair with him. Meanwhile, William and Joan panic when J-Spot has trouble bringing in customers. They hope to correct this by giving the place an air of exclusivity.
Doug lures Carrie to a timeshare sales ski weekend where the strength of their relationship is tested under the intense sales pressure. On the same excursion, Spence and Danny feel the sting of intolerance when they assume the role of a "couple" to enjoy the weekend.