The episode begins with David telling his pregnant wife that he does not want to go for the reunion. He says that he spent those four years being totally invisible and now going for the reunion seems like torture to him. His wife convinces him to go. Later, David arrives at the reunion. At the gate, he sees Becca, who is distributing the ids. Becca does not recognize David. However, he collects his id and goes into the party. Later, he is standing with one guy and having a drink, when he notices that the party bubbles are leaving behind blood residue when they burst. He checks the dispenser. He then follows the wire to a room and finds a dead body lying on the table. It is Becca; and it is her blood that is dripping into the soap solution.
Next, Finn and Russell arrive at the scene. David tells them that Becca was the queen of the class and she was the one who arranged the reunion. They see that her throat is slit. So, the queen of the class is murdered in a reunion that was held fifteen years after her reign. Robbins examines the body and declares that the COD is due to excessive bleeding. Nick finds a pair of nunchucks and a lot of other things in the room. Greg finds a bloodied fingerprint on the tray holding the soap solution and infers that the killer might have used the soap solution to clean his hands. This means that the trace from the killer was carried around by the bubbles, which could have landed anywhere and placed it on anyone.
Robbins finds a small glass piece on Becca’s palm. Morgan talks to Kelly Nivens, who says that she was very close to Becca, but they had lost touch. She has a red stain on her dress and Morgan takes a picture. Jim talks to Grady Foster, Becca’s husband. He tells Jim that Becca had lost touch with all most everyone at the party. He says that he was tired of all the hosting and stuff and so he decided to take a table and have his drink.
Finn talks to Janet, who is an attorney in Manhattan and she tells Finn that Becca was the kind of person with no big ambitions in life. Nick is still examining the crime scene and he sees some glass pieces on a copier. He pulls up the tray and finds that the glass is cracked. He then prints the last action that was in queue. He looks at the printout and is shocked to see Becca’s face pushed against the glass. The other printout shows two hands struggling/fighting for a piece of paper. Next, David is examining Becca’s body in the lab and he imagines Becca’s dead body talking to him. He goes out to get some air. Nick goes through the pictures of those present in the party and compares it to the printout. He notices that Kelly’s bracelet looks similar to the one in the printouts.
Next, Russell interrogates Kelly. She admits that she was at the copier and had a fight with Becca. She says that Becca was up to her old tricks. She then tells him about Becca’s Bingo cards that she handed out to everyone at the party. It has a list of “quirks” and the people at the party were supposed to give names of the classmates who had them; and the quirks were klepto, bed wetter, six kids six fathers, bulimic etc. Kelly knew that Becca was a gossip queen and Kelly did not want to destroy the party. Kelly also tells Russell that Becca’s husband, Grady Foster is her therapist and she poured out all her secrets to him. She did not know that he was Becca’s husband till they arrived at the party.
Kelly reveals that she is a “kleptomaniac” and she is also sure that he knew the secrets of the others from the party. She tells Russell that she did not kill Becca. Next, Finn tells Russell that Grady refused to divulge the names of his patients. They look at the pictures from the party and Russell infers that “Klepto Kelly” did not kill Becca. They also know that everyone who was on the Bingo card had a motive to kill Becca. The only way they could get a list of suspects is with Grady’s help. Nick has figured out a way to get the list of patients.
He shows Russell the surveillance footage in front of Grady’s clinic. It records all the cars in the parking lot. They can track the patients with the license plate numbers. Nick notices that Becca also arrives at the clinic a little late in the evening when the clinic is empty. The camera records her stealing some files from Grady’s office. Later, Grady arrives at the clinic and the two of them have an argument. Jim questions Grady once again. Grady tells Jim that he had no clue that Becca knew his patients till he saw them at the party. Grady always knew about Becca’s pathological hunger for gossip. He says that he never laid a hand on Becca. Greg and Morgan are at the party site, swabbing the bubble residue and Morgan finds a trace on one of them.
Jim messages Greg about a guy from the party, who is lying unconscious on a playground. Morgan and Greg go to check on this guy and see that he is really drunk. They also see a bloodied handprint on the back of his shirt. They bring him in for interrogation. David knows this guy, Sean McHenry. He tells Nick that Sean was a quarterback and dated Becca for four years. Janet arrives and David is surprised to learn that she is representing Sean. Sean tells Nick that Becca was still into him. They had gone to the room to make out and after a minute, Becca pulled back and said that she wanted to go back to the party. He says that that there was a cut on Becca’s palm and that is how the bloodied print got on to his shirt. He says that he did not kill Becca.
Hodges tells Morgan that the trace she found on the residue is grey paint and they figure out that it is from the ceiling access panel of the room in which Becca was killed. It is right above the bubble tray and someone opened it. Morgan goes to examine the area and finds a bomb. The bomb squad dismantles the bomb and gives the CSI team the non-explosive parts to run tests on. Nick tells Russell that he did some digging and learned that Sean, who was a gym instructor at the junior high, was recently given a pink slip. He feels that Sean was trying to get back at them by blowing up the place. This means the school was that target and not the reunion. The bloodied prints on his shirt anyway make him a suspect. Finn goes to arrest Sean and finds Janet with him (with no clothes on).
Morgan finds the murder weapon in a dumpster next to the liquor store where Sean bought the liquor from. Henry tests the blood on it and confirms that it is Becca’s. He says that the blood was too dry and it is rather unusual. Morgan infers that there is more to the story. Greg is working on some plaster pieces that were found with the bomb. He puts the pieces together and it seems to form a face. David recognizes the face. It is Caroline and she killed herself during high school. David tells his team that the seniors, Sean and Becca always made fun of her. They had made the mask and hung it on the college walls for fun. Hodges arrives and tells them that the print that he found on the bomb’s duct tape is a match to Max Dinello.
David says that Max was Caroline’s friend. His prints were also on the escape panel. Greg arrives and tells them that Max is a teacher at an alternative school for troubled teens. He shows them the website and it has Janet’s picture on it. Janet is no longer an attorney; she is a lunch lady. So, Max and Janet (the vengeful outcast) are working together. Russell thinks that Becca must have caught Max planting the bomb and he must have slit her throat. Janet could be the one who planted it in the dumpster to frame Sean. Next, Hodges tells David that the materials used to plant the bomb are really old and dated back to ’98. He thinks that the bomb was planted in ’98. He strongly feels that Max was trying to diffuse the bomb by pouring liquid nitrogen on it. This explains why the blood on the knife was so dry.
David goes back to the autopsy results and declares that the irregularities in the stomach and trachea were due to ingesting liquid nitrogen. Max is brought in for interrogation. Max admits that he planted the bomb in ’98 to avenge Caroline’s death by killing Sean and Becca, but couldn’t set it off because he felt it was not worth it. He was certain that it would not explode accidentally. At the reunion, he tried diffusing the bomb with liquid nitrogen and Becca entered the room. She accidentally ingested a drop of liquid nitrogen and started choking. Max tried to perform a tracheotomy but Becca did not hold still and she died.
Janet admits that she tried to help her friend and get rid of the evidence. She also admits that she tried to frame Sean, act as his lawyer and also fulfilled her high school fantasy by sleeping with him. Case Closed. Next, David is at the hospital and his wife gives birth to a son. Robbins and Hodges arrive to welcome the new member. The episode ends.