When an anonymous murder confession is found in a modern art exhibit, the team reinvestigates the fatal drug overdose of a sixteen year old high school student and cheerleader in 1997.
On September 1st, 1997, best friends Rainey Karlsen and Celeste Church are trying out for varsity cheerleading. While an outcast named Joe Vives-Alvarez watches in disgust, Rainey and Celeste make the varsity team, much to their delight. Later on, Rainey's dead body is found on the empty football field. Her death was ruled as drug overdose as the case was closed.
In 2007, Lilly and Scotty head over to a museum in the art exhibit, where people confess their secrets after getting a call from Rainey's mother, Elizabeth. In the exhibit is a piece of paper that says "I killed Rainey Karlsen" with a drawing of what appears to be an atom. Now knowing for certain it was murder, Elizabeth insists the two detectives re-open the case in addition to her firm belief that her daughter was too good of a person to take drugs, despite what the autopsy says. Lilly then notices that the atom is the same design that was found on Rainey's leg when she died, confirming enough suspicions to re-open the case.
At the station, the team analyzes the case and Nick remarks that he loved high school because he was a hockey athlete, who the girls admired. Lilly jokes that she was the kind of person who nobody wanted to mess with. Lilly, Nick and Kat review the autopsy reports that said that high levels of Liquid X and alcohol were in her system and no signs of sexual assault. In addition, she missed her high school pep rally. The team ultimately decides to question Rainey's best friend, Celeste. John and Scotty question Celeste, who tells them that she had no idea who was with Rainey before she died. Celeste then tells them that she and Rainey have been best friends through everything, yet she wasn't as popular as Rainey because their cheerleading captain, Becca, chose favorites.
In a flashback, Becca and her friends invite Rainey and Celeste to sit with them now that they're on the squad. Becca jokes about Celeste being fat and decides to invite Rainey to a party, which attracts the attention of Becca's then-boyfriend, Casey Evans.
Celeste reveals that Becca wanted to be friends with Rainey because Becca thought that Rainey would be a threat to Casey. Because of this seemingly manipulative attitude from Becca, the team decides to question Becca.
Birmingham High School is preparing for their ten-year high school reunion. Lilly and Will ask Becca if Casey had the hots for Rainey. Becca then responds that she invited Rainey over to a party because she was a new member of the varsity team. Will asks if there was anyone who was willing to hurt Rainey and Becca answers that it's those who want to hurt good-looking people.
In a flashback, Rainey, Becca, Celeste and Casey are in a physics class taught by Coach Pruit. Coach Pruit then asks a question about which Newton's Law of Motion would be a rock if it stopped one from skateboarding. Casey jokes "my ass" and Rainey raises her hand. Becca then convinces Rainey to discard her answer and tells her that if she looks smart, she'll be a loser. Behind them, Joe berates them for being idiotic and suggests to eradicate themselves from the world. Rainey seemingly takes this more offensively than Becca.
Lilly and Will are skeptical to think that Joe killed Rainey just because Becca thought he was a loser. However, Becca then tells them that Joe was expelled from school a few months after Rainey's death. Rumor has it that it was Liquid X.
Nick and Scotty question Joe and remind him that he wanted Rainey to be eradicated from the world. Joe defends himself and says that while he was expelled from school, it wasn't from Liquid X; it was because he got caught smoking marijuana for a fifth time on the bleachers. Joe then proceeds to tell them that he was wrong about Rainey and thought that she was better than the popular kids, including Casey, who was always wanting to get with Rainey.
In a flashback, Rainey confronts Joe and then confesses that her answer in the physics class was Newton's First Law of Motion--an unbalanced force. Joe is surprised and asks her why she would take Becca's advice earlier and Rainey responds that he wouldn't understand. Joe then tells her how to deal with peer pressure and Rainey says that cheerleaders look cool and that maybe it's stupid and shallow to want it. Joe then assures her that something like that is what everyone would want. Casey then interrupts them and places his hands on her shoulders, making her uncomfortable. Joe tells Casey to stop and Casey demands who he is. Joe looks at Rainey, who doesn't say anything and grumbles that he's a no-one.
Nick asks Joe if Casey might have killed Rainey and Joe tells them that in Casey's college years, he was charged with date rape. John and Lilly then bring in Casey for questioning. Casey tells them that the date rape charges were dropped and doesn't seem to be worried. Lilly asks him where he was on the night of Rainey's death and he answers that he was partying with his friends at his house because his parents were out of town. John asks if Rainey told him to get lost, but Casey tells them that she didn't tell him to get lost, but someone else.
In a flashback, Casey and the rest of the football team are hiding in the girls' locker room, where Becca and the rest of the cheerleaders walk in after a big game. Becca congratulates Rainey and Celeste on their first game and prepares them for a tradition after their first game. The tradition is that first-time cheerleaders have to French kiss each other. Rainey doesn't want to, but Celeste merely pecks Rainey on the lips. Casey and the football team emerge and chant "TONGUE!". Rainey panics and tries to run out of the locker room and finds that Coach Pruit is also with the team. Angered, Rainey threatens to tell the principal on him before storming out, leaving Celeste with the rest of the team.
Casey remarks that Coach Pruit was a "cool guy" and bought the team beer on occasions. After hearing this, Lilly and John are lead to believe that Coach Pruit killed Rainey to shut her up before she could tell the principal about him.
Kat and Will enter Coach Pruit's present day classroom to question him about Rainey's death and remind him that Rainey threatened to report about him in the girls' locker room. Coach Pruit tells them that she didn't report him, but she did teach him a lesson on the day of her death to stop being friends with students and do his job. Coach Pruit then tells Kat and Will that he learned this on the day of the pep rally, just right before she was last seen.
In a flashback, Coach Pruit's a bit impatient with one of the student's presentation during physics class. In the classroom, Casey makes a suggestive gesture to Celeste, who is teary eyed, much to Becca's disgust. After the student's presentation, it's Becca's turn. Becca gets in front of the class without a poster board and makes a suggestive comment on friction and lubrication. The class applauds and Coach Pruit approves while Joe scoffs in the back. Rainey then calls out on this and says that Becca's "presentation" is nowhere near a coherent discussion. Coach Pruit ignores this while Joe is fascinated to see someone finally stand up and Rainey then proceeds to call Coach Pruit out on how he teaches and takes advantage of his job. Coach Pruit ignores this and threatens her with detention. Angered, Rainey storms out of the classroom, saying that Joe is the only sane person in the classroom. Joe applauds while Becca jokes about what just happened. Annoyed, Joe flips over his desk and storms out as well.
Coach Pruit tells Kat and Will that Rainey was right all along and that he should take his job more seriously. Kat then asks if Joe walked out of the classroom after Rainey and where was his desk. Coach Pruit then points out where Joe sat that day. On the desk, where he sat, Kat and Will find a drawing of an atom in permanent marker.
Joe is brought in for questioning again and Lilly and Scotty confront him. They present Joe a photo of his desk, where he drew the atom. Joe admits that he drew that, but then Lilly presents a photo of the atom on Rainey's leg and accuses him of killing her. Joe then displays a look of despondency and reluctantly says that he was the one who wrote the note in the museum and he killed Rainey. Seeing through this false confession, Lilly and Scotty asks why he would admit to Rainey's murder. Joe answers that it's their ten-year reunion and nobody thinks about her or cares about her. Joe then blames himself for her death, calling himself the "unbalanced force".
In a flashback, Rainey is sitting outside the school away from the pep rally during the evening. Joe then finds her and sits next to her. Rainey tells him that because she intentionally missed out on the pep rally and contemplates on quitting the squad, but is worried that Becca would then humiliate her throughout her high school days. Joe then draws an atom on her leg, explaining that she wouldn't want to be the orbiting dots, getting tangled with no beginning or end. Instead, she'd want to be in the center--sitting, constant and observing. Joe explains to her that he draws this to help him. Inspired, Rainey asks if two centers can be friends and Joe agrees to the idea. The two share a kiss and Rainey tells him that she's going to quit the squad. As Rainey walks off, Joe reminds her that it's only high school.
Joe confesses that he didn't tell the police that he was with her the night she died because he was the "bad druggie kid" and nobody would've believed him, making him the scapegoat for who most likely killed her--Becca.
At the reunion, Lilly confronts Becca, who tries to avoid her. Lilly tells Becca that this reunion was just so Becca could feel great again and relive the glory days as well as calling out on her two failed marriages (going on three). Lilly reminds Becca that Rainey was going to quit the squad and show the world how much of a loser Becca was. Becca retaliates and tells Lilly that she showed Rainey who's boss.
In a flashback, Becca and the other cheerleaders, including Celeste, are about to pour one dose of Liquid X into their beer cans out on the empty football field at night. Becca then makes another joke about Celeste being fat, causing Celeste to pour all of the Liquid X into her beer without anyone's notice. Rainey then approaches and calls Becca out on her manipulative and cruel methods towards other people. Rainey announces that she's quitting and walks away. Angered, Becca orders her friends to grab Rainey and pin her down to the ground. Becca then snatches Celeste's beer, not knowing that it's completely spiked with Liquid X. Becca then force feeds Rainey the beer down her throat and Rainey starts to convulse. Panicked that she "only had one beer", Becca and her friends flee leaving Celeste behind with Rainey.
Lilly then catches that Becca grabbed Celeste's drink, thus confirming Becca to be responsible for the murder of Rainey.
Away from the reunion, Will and Scotty find Celeste in a classroom in the dark. Will asks her if this is to make peace with what happened and why she drugged her own beer with so much Liquid X. Celeste answers that she just wanted to fit in. Will and Scotty remind her that Rainey was her best friend, but Celeste says that Rainey abandoned her in the locker room, where it's implied that she was raped. Rainey found out and was going to tell everyone, destroying Celeste's popularity. Celeste confesses that "she paid too high a price" to be a cheerleader.
In a flashback, Rainey is dazed by so much consumption of the Liquid X and alcohol. Celeste tends to her and Rainey tells her to step away from everything she went through, especially that what happened in the locker room "wasn't just kissing". Celeste insists that she doesn't say anything otherwise she'll lose everything and be nobody. Rainey reminds Celeste that was always somebody to her. Feeling fainter by the second, Rainey tells Celeste to call an ambulance. Celeste reluctantly lies that she already called an ambulance and that they'll be arriving very soon. Feeling assured, Rainey looks up into the sky and sees the stars in the same pattern as the atom that Joe draws. Rainey then loses consciousness and dies in Celeste's arms as Celeste starts crying.
In the present, Celeste is likely taken under arrest. In addition, Lilly is escorting Becca out of the reunion in handcuffs in front of her classmates, including Casey as well as Coach Pruit. At the art exhibit at the museum, Elizabeth Karlson pins a piece of paper that says "my daughter is my hero" before leaving. As the case folders are being put away, Nick shows Kat a picture of him back in high school and the two share a laugh of how he looked back then. At the reunion, Joe looks into the night sky to see the stars as the same as the atom. He then sees a ghostly image of Rainey Karlsen, who smiles at him.
- Kathryn Morris as Lilly Rush
- Danny Pino as Scotty Valens
- John Finn as John Stillman
- Jeremy Ratchford as Nick Vera
- Thom Barry as Will Jeffries
- Tracie Thoms as Kat Miller
- Whitney Able as Rainey Karlsen
- Veronica Lauren as Celeste Church (2007)
- Adam LaVorgna as Joe Vives-Alvarez (2007)
- AnnaLyne McCord as Becca Abrams (1997)
- Drew Powell as Casey Evans (2007)
- Robin Pearson Rose as Elizabeth Karlsen
- Lauren Woodland as Becca Abrams (2007)
- This episode uses some elements from the film Mean Girls.
- A close inspection of the report when Lilly and Scotty examine the note on the wall shows the dialogue, even the personal remarks, from the following scene.
- Sponge "Plowed"
- Spice Girls "Wannabe"
- Toad the Wet Sprocket "Something's Always Wrong"
- Toad the Wet Sprocket "Crazy Life"
- Hole "Doll Parts"
- Closing Song: Radiohead "High and Dry"