As the episode opens, we hear a commotion inside a darkened, suburban house. A man is running from the house; his face is cut and bleeding. He makes it outside to the lawn, but turns around to see that his attacker is outside with him. He pleads with the attacker not to hurt him and says he "doesn’t know anything else”. As the attacker approaches, we see that it is Charlie Bradbury. She tells the man that she knows he doesn’t know anything else, but plans to torture him anyway. She smiles cruelly at the man.
At the bunker, Sam is in the library talking to Castiel on his cell phone. We hear Sam ask Cas to keep him posted with any updates. As Sam is talking, Dean enters the room carrying two plates of food. He puts one down in front of Sam and sits down across from Sam with his own food. During the discussion that follows, we learn that Dean has decided that clean living will help him fight the Mark of Cain, so he has been getting more sleep, has not been drinking any alcohol, and is eating healthier – as indicated by the egg white omelets he has made for himself and Sam. Sam eats his omelet happily, commenting that it tastes “awesome”, but Dean doesn’t like his, and pushes it away.
Unhappy with his current “commitment” to clean living, Dean is disappointed to hear that Sam doesn’t have any new information on the Mark. Hours pass, and we see the Boys reading volumes from the bunker’s library and researching on their computers, trying to learn anything that might be helpful. As they are working, Sam comes across a shocking video that looks like Charlie beating someone up. We see that it is the man we saw at the opening of the episode. Apparently, a neighbor videotaped the attack. In shock, the Boys watch the tape. Dean is surprised that Charlie is back from Oz, and confused that she didn’t call them; he tries to call her, but she doesn’t answer. Meanwhile, Sam investigates the man Charlie was beating. He is Peter Harper, a district attorney from Topeka, Kansas. Sam also reports that a court stenographer from the same town was also attacked. Sam is shocked by the video, but Dean asserts that they really don’t know what they’re looking at. He insists that Charlie could be working a case, and that taken out of context, what they do when they are working doesn’t look much different. They agree to head to Topeka to investigate.
As they are preparing to leave, we see Dean in his room packing his weapons bag. He picks up a knife and his hand starts shaking noticeably. His back is to the door, so Sam doesn’t see the shaking when he comes to Dean’s room to see if he’s ready to go. Dean doesn’t tell Sam about the shaking, and hastily throws the knife into his bag so they can leave.
In Topeka, Sam and Dean are in their fed suits interviewing Peter Harper. He denies noticing anything unusual the night he was attacked. He tells the Winchesters that the woman who attacked him wanted to know about a case he'd worked on several years ago. It was a car accident in which a drunk driver hit another car. One occupant in the other car was killed, and the other was severely injured and declared brain dead. Dean and Sam recognize the details of the car accident that involved Charlie’s parents. When they mention the Middletons and their 12-year old daughter to Mr. Harper, he seems surprised that they know about the case, but the Boys tell him that they “do their homework” at the FBI, so he accepts their answer. Harper tells them that the case never went to trial, and that it was removed from the books and all the files were sealed. Sam and Dean seem reluctant to believe him. He insists that he looked into the case again after his recent beating, but there’s no new information. All he could find was a social services file on the surviving daughter. He gives the file to the Winchesters, and we see that it is about Charlie.
As the interview continues, Harper denies that he can remember anything else about the case, but Dean and Sam clearly don’t believe him. Sam tells Harper that the court stenographer that was attacked was only released because she gave up his name, so he suspects Harper must have also given up a name. Harper denies this initially, but after being threatened by Dean, Harper reveals that he was paid a lot of money (from offshore bank accounts) to make the case go away. He tells them the name of a councilwoman who was involved.
Later that day, we see the Winchesters driving to the councilwoman’s house to interview her. As Dean is driving, Sam looks over Charlie’s file. We learn that her real name is Celeste Middleton, and that she may be going after the people who destroyed her family. Dean insists that they have to find Charlie before she does something nobody can walk away from.
They arrive at the councilwoman’s home to interview her, but she brushes them off and refuses to talk to them, so they stake out her house, assuming that Charlie will come for her next. As they are waiting, Sam continues to look through Charlie’s file and learns that she was diagnosed with some psychological problems when she was younger. Dean says that if someone looked at their juvenile files, they would both have some unfavorable diagnoses as well. He insists that Charlie is a good kid and there must be an explanation for what she’s doing. As they are talking, a loud crash and a scream erupt from the councilwoman’s house.
Dean and Sam rush into the house with guns drawn and find Charlie holding a knife to the woman’s throat. They try to talk Charlie into releasing the woman, but she taunts them and refuses. Finally, Dean and Sam put their weapons away, since Charlie knows they are not going to shoot her. Charlie shoves the woman at Sam and runs off. Dean chases Charlie and tackles her. They wrestle briefly, but she gets away. Meanwhile, Sam asks the councilwoman what information she gave up, and the woman tells him that Charlie wanted her bank statements. As this is happening, Dean has chased Charlie outside just in time to see her driving away in an SUV. She has slashed one of the Impala’s tires, so he can’t follow her. Dean watches in frustration as Charile drives away, but is then shocked when another Charlie drives up in a different car. As this is happening, Sam rushes out of the house in time to see the second Charlie. Realizing that the Boys must have seen her twin, Charlie says “we should probably catch up.”
At a bar, Charlie tells the Boys that there are now two Charlies –one “good” Charlie and one “bad” one. They asked how this happened, and Charlie tells them that there was a war in Oz – the war for Emerald City. She says their side was losing the war, so she made a deal with the Wizard of Oz, who told her that in order to win the war, she would have to release her true “darkness”. The Wizard used the “inner key to Oz”, which opens your soul, to release Charlie’s dark side. DarkCharlie won the war single-handedly, but she did some terrible things to accomplish that. Charlie also tells the Winchesters that the two parts of her are still connected physically, so if one of them gets hurt, so does the other one. Charlie says that all her darkness is with DarkCharlie, so she can only do good things, which is very difficult.
Charlie tells the Winchesters that DarkCharlie is seeking revenge to win her back. Charlie says she has been following DarkCharlie so she can lock her away forever, but Sam says that won’t solve the problem. The Boys suggest that they get the key from Oz and put DarkCharlie back, but Charlie tells them that DarkCharlie broke the key, so there’s no way to get back to the Wizard. Sam suggests that they find DarkCharlie before she gets to the person she’s looking for. He suggests that since she’s following the money trail, they should hack the bank records to see who was paying people off to make the case go away. Charlie says she can’t hack into anyone’s bank accounts, because hacking is “bad”, so Sam convinces her to show him how to do it. Dean goes over to the bar to get refills for everyone (non-alcoholic beverages) and we see that his hands are still shaking.
Time passes, and we see Sam, Dean, and Charlie at the bar continuing to look into the case. They learn that the payoffs were all diverted through a series of dummy organizations, but all the money leads back to a man named Russell Wellington, a wealthy real estate executive. They learn that Wellington’s car was reported stolen the week of the Middleton's accident, and he temporarily went on sabbatical from work, only to show up two weeks later with bruises and a broken ankle. They surmise that Russell Wellington is the man who hit Charlie’s parents. Dean agrees to try to protect Russell from DarkCharlie, while Sam and Charlie return to the bunker to look through the Men of Letters’ files on the Oz key to see if there is a way to fix the key.
Dean stakes out the real estate office until he sees Wellington arrive. Then, he goes into the office and pretends to be a client. He waits to be seen and stalls his way through a meeting with Wellington, but eventually Wellington loses patience and tells Dean to leave. It is evening by this point. Dean refuses to leave and tells Wellington that he is there to save his life. He tells Wellington that he knows about the car accident and the payoffs. Wellington is indignant and protests, but as he is arguing, the lights go out. Dean tells Wellington to stay in his office and goes into the outer waiting room. As soon as Dean leaves, Wellington tries to use the phone, but it is dead.
Dean finds DarkCharile in the waiting room. He tries to convince her not to kill Wellington. DarkCharlie tells him that she doesn’t want to hurt of kill Wellington – she says she just wants to talk to him and tell him what he did to her life. She begs Dean not to interfere, saying that she deserves a chance to tell Wellington what he did. To make her point, she gives her knife to Dean and insists that she’ll hand Wellington over to the police as soon as she’s done talking to him. Dean is skeptical at first, but when DarkCharlie surrenders her weapon and seems sincere, he allows her to go into Wellington’s office while he waits outside.
Inside the office, Wellington recognizes Charlie. He apologizes for what he did, and says that he’ll turn himself in to the police. DarkCharlie says she forgives him, and Wellington relaxes a bit. But then DarkCharlie closes and locks the door. Before Dean can break the door in, DarkCharile stabs Wellington in the heart with a letter opener that was on his desk, and escapes out the window.
Meanwhile, at the bunker, Sam and Charlie discover a Man of Letters named Clive Dillon. He is the one who originally discovered the Oz key. Dillon went to Oz, but left the key on Earth. L Frank Baum found the key and went to Oz to rescue Clive and Oz. That’s when Dorothy tagged along for the ride and got stuck in Oz. After Baum rescued Clive, Clive came back to Earth and retired from the Men of Letters. The Men of Letters changed Dillon’s identity (to Michael Carter), and he ended up living in a nearby town. Sam questions how Dillon is still alive, since he’d be over a hundred years old, but Charlie tells Sam that time is different in Oz. Charlie and Sam leave to go question Dillon.
As Sam and Charlie are on their way to Dillon’s house, Dean calls them to tell them what happened. As they are talking, Sam tells Dean that they are heading to see Dillon (aka Carter) in Junction City. Sam texts Dean the address and they agree to meet there.
Next, we see Dean in a bar (presumably near the place where Wellington was killed). He has ordered a shot of whiskey and is considering drinking it when DarkCharlie shows up. Dean confronts DarkCharile about lying to him and killing Wellington, but she insists that he lied to himself,because that's his way. Dean tells DarkCharlie that she will pay for what she did, but she insists that Wellington got what he deserved because he was the monster – not her. She insists that being dark set her free, and she challenges Dean to admit that he feels the same way. Dean tells DarkCharlie that she won’t be around for long, because a former Man of Letters in Grantsville is going to help them fix the Oz key and put her back where she belongs. DarkCharlie sneaks away from Dean, steals his car and leaves. Minutes later, Dean realizes she’s gone and rushes outside in time to see her drive away in the Impala. He calls Sam to tell him what happened, and that he told her Dillon lives in a different town, which should buy them some time. He steals a car and heads to Dillon’s house.
Meanwhile, Sam and Charlie arrive at Dillon’s house. At first, Dillon denies who he is. But when Charlie shows him the broken Oz key, he admits his identity. As they are talking, Dillon says that the six Oz keys are forged from Oz steel – they can only be repaired back in Oz. Sam asks Dillon more details about what happened to him while in Oz. Dillon admits that a coven of witches captured him and used the inner key to release his dark side, who was evil and power hungry. Dillon’s dark side eventually became the Wizard of Oz. Charlie tells Dillon that Frank Baum’s daughter, Dorothy, runs Oz now and the Wizard is by her side. With Dorothy being in danger, they must find a way back to Oz. As they talk, they realize that there is no way to return to Oz and find the Wizard, but there is a way to being the Wizard to Earth. Dillon tells Charlie and Sam that if he is mortally wounded, the Wizard will have to come to Earth to save them both. After a brief discussion during which Dillon blames himself for unleashing the Wizard in the first place, he pulls a gun out of a drawer and shoots himself.
Next, we see that Dean has arrived at Dillon’s house in time to hear the gunshot. He prepares to rush inside, but DarkCharlie has also arrived – apparently having followed Dean to the location. Dean tells her that he will not let her inside and will keep her away from Charlie; after she taunts him and attacks him, they begin to fight.
Inside the house, Dillon has shot himself in the chest. As he is lying on the floor, a mirror in the room begins to glow bright green before shattering. The Wizard, wearing a dark cloak and mask, steps out of the mirror. We see that he has a scar on his cheek that is identical to a scar on Dillon’s cheek, proving to us that they are the same person. The Wizard is angry with Dillon for allowing himself to get shot, since his only task all these years was to stay alive and in doing so keep them both alive. Sam tries to shoot the Wizard, but the Wizard uses telekinesis to fling Sam’s gun from his hands. Then, he uses his magical powers to bind Sam’s hands and feet with green bands of light. Sam falls to the floor, unable to move or remove the bonds. As this is happening, Charlie suddenly shouts in pain and grabs her face. We see that her mouth is bleeding, and realize that Dean and DarkCharlie are outside the house fighting. Every time Dean hits or injures DarkCharlie, Charlie feels it. The scene briefly switches to the fight outside, which has grown more intense.
Sam begs the Wizard to release him, so he can help his friend. The Wizard refuses, telling Sam that his friend wanted to be a hero, and heroes die. As he says this, he extends a hand toward Sam and we see that he is using his powers to strangle Sam. As this is happening and the Wizard is distracted, Dillon tells Charlie to kill him. She refuses at first, but he tells her that he forgives her. As Sam struggles to breathe, Charlie shoots Dillon. The Wizard falls over dead, with a bullet hole in his face. Sam’s mystical bonds disappear, but suddenly Charlie is in a great deal of pain. Sam grabs the keys from the Wizard’s belt, and tells Charlie to hang on.
Outside, Dean and DarkCharlie fight viciously, until Dean breaks her arm and overpowers her. Eventually, DarkCharlie ends up on the ground, with Dean kneeling over her and repeatedly punching her in the face. As this is happening, Sam suddenly appears outside, carrying Charlie, who is still conscious, but bleeding and in pain. Sam shouts at Dean to stop. Dean stops, seemingly confused about how he ended up in his current position.
Sam gently lays Charlie on the ground next to DarkCharlie. He puts the key from the Wizard’s belt in Charlie’s hand and steps back. As the two Charlies lie on the ground, they speak briefly. DarkCharlie presumes that Charlie has killed the Wizard. She says she knew Charlie was capable of that all the time. As the key begins to work, a shimmering, ghost-like light rises above DarkCharlie’s body and settles over Charlie’s body before being absorbed into it.
Once the process is complete and Charlie is “whole“ again, Sam rushes over to her. As Sam kneels on the ground cradling Charlie, who is crying, Dean stands away from them, apparently ashamed of what he has done. He looks at the blood on his hands, and notices that his hands aren’t shaking anymore. He seems saddened, or perhaps ashamed, by the revelation.
Back at the bunker, a few days have passed, and Charlie has apparently been resting and recovering. Sam is in the war room talking on his cell phone to Cas. We hear Sam tell Cas that Dean is “better” or at least calm, but they have to do something about the Mark. He says that they have to find Cain or find something else to help Dean.
Sam hangs up as Charlie enters the room. Her bag is packed and she is preparing to leave. Her left arm is in a sling and her face is bruised, but she is up and around. Dean is reading a book in the library; his face is also cut and bruised. They look at each other briefly from a distance, but don’t speak.
Sam asks Charlie how she feels, and her response is that she feels “balanced”. She asks if there’s any news about the Mark. Sam shows her a fact sheet on a book he found called the “Book of the Damned”. The book is supposedly in a library in Tuscany. Charlie agrees to look for the book. She says there’s no going back to Oz, but with the Wizard gone, Dorothy will be fine. She says that DarkCharlie is “quiet”, but they all need to keep moving forward. As she is speaking, she looks over to Dean and walks into the library to talk to him.
Charlie tells Dean that she won’t let what happened to her happened to him. When Dean says it’s already happened, Sam reminds him that Cain found a way to live with the Mark, so he can, too. Dean is skeptical, but Charlie reassures him. She also says she forgives him. Dean stands up, hugs her and apologizes. Charlie’s response is “then prove it”. Charlie hugs Sam, grabs her bag, says goodbye, and leaves. After Charlie leaves, Sam asks Dean if he’s okay, and Dean says “no”. Sam tells Dean that Charlie is right, and they can “do this”. Dean says “well then, let’s get to work”. We see him look down at his hand again and notice that it is not shaking – yet.