The sophomore prom has ended. Well, the school-sponsored part of the night is over, anyway. The drama, however, is only just beginning.
The season finale opens with Naomi in the bathroom, telling her sister all about Liam's difficult childhood. Their conversation is interrupted by Phoebe, who begs Naomi to step up and throw the after-party, since Principal Wilson found out that it was supposed to be at Phoebe's house. Jen tries to say no to a party in her house, but Naomi argues that since she bought everything and is the only one paying rent, she's allowed to call the shots. Which means the party is a go. Jen warns her sister that she doesn't want to do this, but Naomi ignores her and goes to spread the word. She is mid-conversation with Annie when she gets a text about Adrianna going into labor. She asks Annie to take care of the party so she can go to the hospital, and Annie agrees.
Outside, Annie finds Dixon, Silver, and Ethan searching for their limo. She tells them that Adrianna and Navid probably took it. The four of them get a ride with some guy named Duncan and his friends – a group which includes Phoebe, who is still angry at Annie for supposedly ratting her out.
Naomi gets a ride to the hospital from Liam. She apologizes for having to ditch him, but he assures her that he'll see her at the party later. He also mentions that everything he told her earlier should stay between the two of them. Naomi promises to keep his secret.
At the hospital, Navid is desperately trying to get the attention of the receptionist, who is gossiping on the phone. She sees his black eye and assumes he's there because he got in a fight, and she tells him it's not urgent and to take a seat and be patient. Navid hangs up the phone and yells at her, telling her that Adrianna is having a baby.
Harry, Kelly, and Debbie are at the "post Prom-a-palooza," the alcohol-free after-party, when they receive word that Adrianna is in labor. They hurry to meet her at the hospital, but Harry makes sure to grab some brownies from the snack table before they leave. He shares them with his wife while they sit in the waiting room. Later, they ask Navid if he knows where Annie and Dixon are. He says no, but it's obvious he's lying. Harry and Debbie realize that their kids are probably at an after-party. And then they just start laughing. Because those brownies? They had pot in them. Of course. They're trying to figure out what to do when Kelly finds them in the waiting room. They tell her what's going on, and she assures them that they have good kids who will be fine, and then agrees to go get them some snacks. She touches Harry on the chest as she talks to him. As soon as she's gone, Debbie blurts out, "she has a crush on you!" Harry tells his wife that she's being ridiculous. But later, when he's passed out on the couch, Debbie is talking to Kelly and mentions her paranoia. She blames it on the pot, saying she always gets paranoid when she's stoned. The look on Kelly's face makes it abundantly clear that Debbie's suspicions are not completely off-base, though.
Navid and Naomi are already in the room with Adrianna when Kelly rushes in. Adrianna is freaking out because Brenda is supposed to be there (apparently she's in China), and because nothing is ready for the baby – she was supposed to have three more weeks. She's telling Kelly all of this when the baby's heart rate suddenly drops and the doctor announces that he's going to have to perform an emergency C-section.
Afterwards, Navid is holding the baby – a girl – and Adrianna is lying on her side with her back to them, looking extremely depressed. Navid asks her if she wants to hold the baby. She says no and tells him to just take her out of there. Navid complies, and heads out to the waiting room to tell everyone the news. He also says goodbye to Naomi, who needs to get back to her place to take care of the party. As she leaves, she passes Ty in the hallway. He is there to drop off his parental waiver, and he has also brought Navid a cigar. Ty tells Navid that he respects him, and thanks him for being there for Adrianna through everything.
Adrianna is still lying in bed when suddenly Brenda walks in. She's dressed like Cleopatra and acting very strange. She asks Adrianna to go for a walk with her, and the two of them find themselves standing outside a room marked "Jim Walsh." Adrianna asks whether he's a relative, and Brenda tells her that he is her father, and that he's dying. Then a dragon randomly shows up, Brenda disappears, and Adrianna wakes up. Something about her dream affected her, and she heads down to the nursery to find her baby. The two are in bed together when Brenda shows up for real. Adrianna has barely said hello when Navid comes in to tell them that the adoptive parents have arrived. Adrianna starts crying. She tells them she doesn't know how she's going to say goodbye and that this is why she didn't want to hold the baby in the first place. Brenda assures her that she's doing the right thing, that adoption is a wonderful gift, and that she knows this from experience. It turns out she was in China adopting a little girl. Adrianna manages to hand the baby over to Leslie and Greg, though she's still crying as they walk out of the room.
Back at Naomi's house, Ethan and Dixon are watching Silver dance. Dixon mentions that having a relationship with Silver is difficult, and Ethan responds by listing Silver's many attributes. Then he saves face by adding that Dixon and Silver make a great couple. Dixon tells him he's right, that they're in love. He walks towards his girlfriend. Ethan, left alone, looks upset as he pulls a picture of Silver out of the pocket of his tuxedo.
Later, Silver also turns to Ethan for relationship advice, and Ethan advises her to keep working at it. They hug, and as she pulls away, Silver asks if Ethan is wearing Dixon's jacket. Apparently they accidentally got switched at some point during the evening. Ethan finds Dixon at the DJ booth and trades back without taking his picture of Silver out of the pocket. Dixon finds it and confronts Ethan a while later, asking him how long he's had a thing for Silver. The two of them are having a heated discussion when Silver comes over to tell them that they have to come swimming. She notices the looks on their faces and asks what's going on. Dixon tells Ethan to admit it, and finally Ethan turns to Silver, tells her he likes her, and then walks away. Silver comes after him and asks him what's going on. She thought they were just friends. Ethan kisses her, then pulls away and tells her that he doesn't want to be just friends. He wants to be something more or he doesn't want to be anything. Then he asks her why she's outside talking to him instead of inside with Dixon. She says nothing.
Annie is having a difficult time trying to keep the party under control. As she cleans up a spilled bowl of pretzels, she has a weird encounter with Jen, who acts like this is all Annie's fault. Later, Annie finds Liam sketching in the backyard. She asks what he's doing, and he shows her his drawing, explaining that he drew her erupting like a volcano. Annie goes back into the house, where she finds Phoebe vomiting in the bathroom. Phoebe asks Annie to drive her home, and Annie says yes, though it's obvious she doesn't want to.
While Annie is gone, Jen is getting her revenge on Naomi. She introduces herself to Liam as Zelda, the next door neighbor. She also mentions that she knows about the tough life he's led, and when he asks how she knows that, she tells him that she overheard some gossipy girls talking about it, hinting that Naomi has been telling people already. Her plan is effective in getting Liam mad at Naomi, and she pulls him inside by the hand. When Naomi gets home from the hospital, someone tells her that Liam us upstairs. She finds him in her bedroom, pulling his pants back on. He won't tell her who the girl is, but Naomi is pretty sure she's figured it out when she finds Annie's sweater lying on the floor. She leaves the room, furious, and Jen steps out of the bathroom. She admits to Liam that she is actually Naomi's sister and he calls her a bitch. That night, after he gets home, Liam tries to call Naomi to explain things, but as he's leaving her a message two huge men storm into his bedroom and drag him out of bed, telling him that his shenanigans stop now: his stepfather is sending him to a "wilderness therapy program."
Downstairs, Naomi confronts Annie about supposedly sleeping with yet another of her boyfriends. Annie denies it, but Naomi causes a scene, which causes everyone else to join her in hurling insults at Annie. They call her a Kansas slut, whisper that she's the one who ratted about Phoebe's party, and one guy even throws a drink in her face, yelling "that's for Charlie!" And just like that, the volcano erupts. Annie's face turns bright red, and she screams, "Screw you, Naomi. Screw ALL OF YOU!" She leaves, stopping briefly outside the front door to call the cops and report underage drinking and to snag a bottle of vodka for the road.
Naomi is inside the house sobbing while Jen consoles her, acting as though she has done nothing wrong when Naomi suddenly sits up, alarmed by the sound of sirens approaching.
Annie is driving down a mountain road when her car suddenly hits something. She stops momentarily, looks at the open bottle of alcohol on the seat next to her, notices another car coming, and drives away. The closing shot is of the other car stopping next to a dark lump in the middle of the road.