Teenage Wasteland is the ninth of twelve episodes in Season Five and the fifty-seventh of the series. Dexter Morgan, now realizing that Jordan Chase is almost certainly a member of The Group, begins investigating his new "friend" in search of evidence to put Jordan on the table. This episode also marks the return of Dexter Morgan's step-daughter Astor Bennett, bringing with her a pile of drama that only a twelve year old can.
Dexter is running on a treadmill, working out with Jordan Chase. Chase tells him that exercise helps bring out feelings, a way to bring out the real him. Dexter and Chase discuss how trauma means getting the opportunity to put yourself together anyway you want. He knows from experience and reveals that he stole it from Plato's symposium (his inspiration for "Take It!"). Dexter sees a chain with a rectangular vial hanging from it with what looks like blood inside. On his way out, Dexter sets up an appointment with Chase for the following day and notices the increase in security. He tells Lumen about the vial and she suddenly sees a shadow at the kitchen door. The knob rattles and she tells Dexter that someone is trying to break in. The door also rattles at the front. Lumen grabs a knife and whispers to Dexter that they are inside and coming towards her. He tells her to keep the line open and hides in the bathroom. It is Astor and a friend of hers, Olivia, thinking the house was empty. They took a bus from Orlando after stealing alcohol from Olivia's house.
Astor begs Dexter not to call her grandparents before leaving to sleep. Harry appears and advises Dexter to get Astor out of there, but Dexter doesn't want to just turn her away. He wants to make things right and be a good father. Harry says that he can do that by turning Astor away.
Deb and Quinn are discussing her meeting with a union representative. Deb thinks she will be fired, but Quinn tells her everything will be okay because she has so many people backing her up who love her, including him. She mentions that he told her that he loves her, but he brushes it off as "just and expression." Deb leaves for the meeting and Quinn tells her to forget he said it. Liddy calls Quinn and tells him about the pictures he took of Lumen and Dexter dumping Cole's body. Quinn is in a bad mood though and angrily tells him that he will call him later.
Dexter asks Lumen's advice on teenage girls. Lumen tells him to talk to her, to share something with her that he did at her age. Lumen tells him to cut her some slack and that the hangover will be punishment enough. Astor comes in and Dexter tells her that he wants to spend the day with her to talk. She agrees as long as Harrison can come too. Just then, Harrison calls Lumen "mama" to everyone's surprise and Astor tells him, "She's not your mama. Your mama's dead." Astor is angry with Dexter now. Olivia remarks that her family is weird too.
Deb has been moved to the file room, but she doesn't feel any better because she is still blamed for the incident at the club. She arrives and tells Francis that Quinn said he loved her but she didn't return the words because she might love him back.
Dexter is back with Chase after another exercise regimen. While Chase showers, Dexter quickly makes a blood slide from the contents in Chase's vial. When Chase returns, Dexter leaves but Chase notices his locker slightly disturbed and a drop of blood. He knows that Dexter has been spying.
Deb has been reading files and finds that there should be multiple suspects for the Barrel Girls case. She tells Masuka and Batista and points out that Cole Harmon should not have been excluded from the suspect list. Batista decides to tell LaGuerta to reopen the case.
Dexter arrives at the lab with the blood sample. Masuka is there and asks about the blood slide. Dexter lies and says that it was supposed to be filed a long time ago. He receives a frantic call from Lumen telling him that Astor and Olivia are gone, but Astor's cell phone was left behind, asking what teenage girl leaves her cell phone behind. Dexter leaves work for home, seeing Lumen speaking with the next door neighbor. He saw the van and part of the license plate number, but did not stop them because he did not know there were any tenants of the house anymore. Dexter calls and reports the van to the police. At the department, everyone rallies around Dexter and is questioned as to where he was when Astor was taken. He admits that he was with Jordan Chase at the time they were taken. Deb warns that Chase hangs with some disreputable people. LaGuerta asks why she says that and Batista tells her that he needs to talk to her about it.
The police has found a man at a gas station with a matching description to the neighbor's information. It is Olivia's father; he followed her after finding Olivia gone by tracing her phone. The girls were found at Bayside being held for shoplifting. Dexter, Deb, and Olivia's father bail the girls out. Olivia doesn't want to leave with her father and Dexter volunteers to take the girls to his house to get their stuff first.
Batista tells LaGuerta about the new evidence found in the file room. LaGuerta finds it very convenient, but Batista urges her to reopen the case. She says that it won't help the department. Batista says that it won't help her.
Dexter brings everyone back to his house, where Lumen is waiting. He uncomfortably introduces Lumen to Deb as his tenant. Lumen leaves to check on the girls while Dexter explains to Deb about his secret relationship with Lumen. Dexter denies anything is going on and Deb leaves. Dexter calls for Astor, asking what is going on with her (drinking, shoplifting). He tells her she is following a bad path and she denies most of everything. Astor turns things back on him, asking about Lumen again. Dexter tells her that they will sit there until she is ready to talk.
Lumen sees bruises on Olivia's stomach, which Olivia tries to shrug off as nothing. Lumen tells Dexter and Astor reveals that she knew and asks Dexter not to be mad. Astor makes Dexter promise not to say anything so that Olivia's father won't hit her anymore. She goes on to say that he only hits her in places that don't show. Astor tells Dexter that she didn't tell him because she thought he wouldn't care. Dexter says that he will take care of it.
Batista tells Deb that LaGuerta won't reopen the case and Deb bursts into her office to confront her. LaGuerta listens as Deb accuses her of many selfish things. LaGuerta says that she made the case go away and mentions that she suspended Quinn to protect Dexter. Deb asks Quinn to explain why he lied about being on vacation when he was really on suspension. Quinn admits to it and explains what happened. He tells her that the composite sketches pointed to Dexter, but that it didn't pan out. Deb angrily leaves him as Quinn ignores another call from Liddy.
Barry meets Dexter outside in the middle of the night and Dexter brings up Olivia's bruises. Barry denies knowledge of them and Dexter volunteers to show him. Dexter continues to hit him and threatens him, telling him to leave his family or he "won't go so easy next time." Harry arrives and Dexter thinks he is going to admonish him, but Harry says that he is proud of him for protecting Astor. He admits that he underestimated Dexter, seeing him as a monster, and that maybe if others had seen that side of him then he might have led Dexter down a different path.
Liddy is waiting at Quinn's apartment and shows Quinn the photos of Dexter and Lumen. But Quinn pays Liddy off and tells him he is done. But Liddy says that this evidence is too big to ignore and suggests taking the info to Deb. Quinn gets angry and tells Liddy to stay away from him and his girlfriend. Liddy only smiles and leaves the apartment.
LaGuerta reopens the case as she promised and Batista tells her that they still have a long way to go before they can share a bed again.
Quinn tells Deb that he loves her and doesn't take it back this time; he would never hurt her. But Deb says that he has hurt her by messing with her brother.
Dexter drives the girls home and Olivia is happy to tell him that her mother mentioned that Barry is officially gone. Her mother greets her at the door with a hug. In the car, Astor asks if Dexter will tell her grandparents about the drinking and shoplifting, but he says that it is up to her because "we all have our secrets". He tells her that he is proud of her for sticking up for Olivia and Astor asks Dexter to tell the truth about Lumen. He continues to deny that she is anything other than a friend who has been through bad things. Astor asks if it makes him feel better about what happened to Rita and Dexter simply tells her that he loves her. Astor doesn't say it back and opens the car door to get her things from the back. When she does, Harrison says "mama" and Astor realizes that he wasn't calling Lumen mama after all. They all go inside to see Astor's grandparents and Cody.
Back at the lab, Dexter finds that the blood from Chase's vial matched a woman named Emily Birch who was not a Barrel Girl victim, but who is still alive. Lumen gets a call from Jordan Chase, who is looking for Dexter. He leaves a message with her, saying that he wants to schedule an appointment to see him. The last thing he tells her is to tell him "Tick, tick, tick. That's the sound of his life running out." He addresses her by her name as Lumen gasps and hangs up.