In 1935, two Men of Letters, arrive at the newly-constructed underground headquarters and activate the system. Once their done, they introduces themselves as James Haggerty and Peter Jenkins. The younger Man, Jenkins, figures that they will soon be at the battle of an epic battle of good vs. evil. Six months later, they're sitting around playing chess and Jenkins is bored. Haggerty take a call from a Hunter, who says that she needs to come in. Once she hangs up, Haggerty tells Jenkins that Frank's kid is coming in, and they're both impressed with what Frank did for his daughter. When the woman, Dorothy, arrives, she is dragging a bag with someone moving around inside. Dorothy asks the two Men if they're going to help her kill the Wicked Witch.
Sam visits Crowley in his cell and gives him a crayon and a piece of paper, and tells him to write down more demon names for the Winchesters to hunt down. Crowley tries to negotiate for better conditions but Sam ignores him and goes out to the main room. Dean returns from dropping Kevin off at a hotel in Bronson to get some R&R, and finds Sam working on a way to help Castiel. Sam wonders why Castiel left but Dean tries to duck the question, and they discuss the table that showed the angels falling. If they can activate it, they can use the system to scan for angels and make sure Castiel avoids them. They follow the cables to a room containing a primitive computer dating back to 1951, with no obvious power source. Dean pries open the back and inadvertently knocks over a jar filled with a blue liquid. When Sam admits that he couldn't find anything about it on the Internet, Dean says that he has an idea. As they leave, the liquid inside the jar breaks out and starts spreading up the wall.
When Jenkins tries to interrogate Dorothy's prisoner, Dorothy tells him that she cut out the Witch's tongue to try and keep her powerless. However, Dorothy warns them that the Witch will soon heal the damage, and that she couldn't figure out a way to kill her prisoner for good. Jenkins figures that the information must be contained somewhere within the archives and Haggerty tells him to go to work.
Charlie comes in response to Sam's call and admits that she got fired a week ago when she linked the news that her company was outsourcing child labor. When they wonder what she's been doing since, Charlie sheepishly admits that she's been hunting, but wishes it was a more magical experience. She works on the computer and informs the Winchesters that it's powered by magic, and can detect magic on a global scale. As she downloads the files, the brothers ask her about her hunting and Charlie admits that she didn't follow the guidelines in the Supernatural brother. Sam is less than thrilled to hear that Becky is releasing previously unpublished novels on Amazon, even though they appear to be written by Chuck. Meanwhile, Charlie warns them that the files are encrypted and it will take a while to decipher them, and suggests that they make themselves comfortable for the night. As they hold a Game of Thrones marathon in Sam's room, Charlie points out that it doesn't look like he's move din yet. Sam tells her that the headquarters is where they work, not their home. When Dean goes to get some beers, Sam asks Charlie what she meant about hunting not being "magical," and the woman explains that while hunting is always magical and glamorous in the books and movies, she hasn't found her quest. Hearing that, Sam warns her that quests suck.
Haggerty and Jenkins are still trying to find a way to kill the Witch when she breaks free. In the struggle she takes care of Jenkins and mind-controls him into attacking Haggerty. As they struggle, the Witch speaks through Jenkins, demanding that they turn over what belongs to her. Dorothy doesn't know what she means and gets directions to the lab from Haggerty. Once she knows where it is, she runs off and the Witch goes after her. Jenkins attacks Haggerty, who is forced to kill him. Haggerty then runs to the lab only to see a bright light burst through the door.
When the trio goes back to the lab with the computer, they discover a green web has grown on the wall. Dean cuts it open and a woman falls out: Dorothy. Charlie checks the archive and discovers that Dorothy was involved in the headquarters' first case. Haggerty never found Dorothy or the Witch after they enter the lab. When Dorothy wakes up, she assumes that they're Men of Letters until the brothers explain who they are and what happened. Dorothy explains that since she couldn't kill the witch, there was only one thing she could do.
In the lab, Dorothy mixes her blood with some chemicals. When the Witch breaks in, Dorothy casts the spell, binding her soul to the Witch and trapping both of them in a jar.
Dorothy warns the others that the Witch woke up when she did.
The Wicked Witch, searching the headquarters, finds Crowley chained up inside of a binding circle. She can't cross the circle, so Crowley tosses her the paper and crayon and tells her to write down what she's looking for.
Dorothy tells the others that she is protected against the Witch but they are all at risk, and that the Witch will seek out the item she was looking for in 1935. The brothers tell Dorothy to help Charlie check the archives for anything useful while they search the headquarters. Once they leave, Charlie complains that Dorothy isn't as nice as she was portrayed in the books. Dorothy explains that her father was a Man of Letters, L. Frank Baum. He went insane and wrote the Oz books with Dorothy as the main characters. When Dorothy complains about how the Men of Letters are just bookworms, Charlie informs her that Haggerty never stopped trying to find her and kept her file open until he retired. Haggerty also found a way to kill the Witch: he made a deal with a fairy to get some poppy extract from Oz. Charlie and Dorothy go off to get the extract and coat bullets with it to kill the Witch.
The Winchesters check on Crowley, who says that he knows what the Witch is looking for. He offers to tell them if they let him "stretch his legs" inside of the circle. They reluctantly unchain him and Crowley shows them a drawing of a key that she made, and says that he lied and told her to go to the kitchen to find it. The brothers go to the kitchen and meet up with Charlie and Dorothy, who explain about the poppy extract. There's only enough for four bullets, and it will only stun the Witch. They load up with the bullets and Sam explains to Dorothy about the key. Dorothy tells them that the key allows the user to turn any door into a portal back to Oz. If the Witch returns to Oz then she will destroying everything that is good and true, using her army of flying monkeys. When Dorothy shows them a drawing of the key from her satchel, Dean recognizes it from when he was doing inventory. He tells the others that it's in his room and he goes with Charlie to get it while Sam and Dorothy stay behind and try to stall the Witch. Once he's alone with Charlie, Dean tells her to hide until it's safe. Charlie refuses, figuring that she's finally found her magical quest.
As they search the headquarters for the Witch, Dorothy asks Sam how long he's lived there. He tells her that he doesn't consider it a home, and that he's never had much luck with homes. The Witch sneaks up on Sam and attacks him, and Dorothy fires one of the bullets at her. Forced back, the Witch transforms into mist and flows into the air vents, and they figure she's heading for Dean and Charlie. Meanwhile, Dean finds the key just as the Witch arrives. Charlie yells a warning just in time but the Witch grabs Dean and knocks him to the floor. She releases a bolt of green energy at him, but Charlie leaps in the way and takes the killing blast. Dean shoots at the Witch, forcing her to retreat.
Dean carries Charlie to Sam's room and lays her down. Sam comes running in and Dean calls to "Zeke," asking for his help. The angel takes over Sam's body and confirms that Charlie is dead, and warns that he doesn't have enough power to bring her back. He can bring her back or battle the witch, and Dean tells him to resurrect Charlie. Once he does, Sam regains consciousness and asks what happened. Dean claims that the Witch attacked Sam and Charlie, and Dean managed to drive it off. Dorothy arrives and Charlie gives Sam the gun with the poppy bullet and go after the Witch. Meanwhile, Dorothy will stay with Charlie until she recovers. As the brothers head off down the hallway, Sam remembers Dean talking about "Zeke" and asks what he meant, but Dean says that Sam must be punchy.
Back in Sam's room, Charlie says that while she was unconscious, she dreamed about her parents being alive. Dorothy tells her that she was in Heaven and dreamed her perfect world. The Hunter says that she died as well when she was in Oz. She got there by stowing away with her father when he went to Oz. They were separated and Dorothy met three freedom fighters. The Witch eventually turned them into a tin man, a lion, and a scarecrow, and then eventually hunted down Dorothy and killed her.
As Sam and Dean search the headquarters, Dean returns to Charlie's earlier question and wonders why he hasn't moved his things in. When Sam doesn't see the point, Dean points out that the headquarters is the closest thing that they've had to a home, but Sam notes that it's never worked out well for him when he's tried to make a home, and he was too young to have any lasting memories of their home before Mary was killed.
Charlie asks Dorothy about the Oz books that her father wrote, and Dorothy explains they were his way of trying to undo what happened to her. The Witch eventually made her way to the real world and Dorothy became a Hunter. Charlie figures that Dorothy's father was trying to pass on clues about how to defeat the Witch, and Dorothy congratulates her on her intelligence. She then says that they have to get to the garage.
The witch manages to grab Sam and uses him as a shield. Dean can't get a clear shot so he leaps on her, but she manages to touch both of them on the forehead. They fall under her spell and the Witch sends them to kill Charlie and Dorothy.
When Charlie and Dorothy get to the garage, Dorothy goes to her old 1935 motorbike that Haggerty saved for her. A pair of ruby slippers are in the saddlebags, and Dorothy explains that they contain magic from Oz. Sam and Dean enter the garage and advance, and Dean grabs Charlie and slams her through a window.
As the witch goes to the headquarters' main door, she speaks through Sam and Dean, telling the women that she plans to summon her armies to Earth. As Dorothy and Charlie struggle with Sam and Dean, the Witch completes her ritual and casts it. The portal opens revealing Oz, and the Witch laughs in triumph.
Charlie kicks Dean in the balls while Dorothy manages to knock Sam back long enough to toss Charlie one of the ruby slippers. She tells Charlie to find the Witch while she keeps the brothers from following.
The Witch waits for her flying monkeys to fly through the portal, while controlling Sam and Dean into overwhelming Dorothy. Her immunity to the Witch doesn't make her immune to the Winchesters, and they prepare to cut her throat. However, Charlie arrives at the portal and rams the heel of the ruby slipper into the back of the Witch's head. She then closes the portal just in time as the flying monkeys arrive, and the door reverts to normal. As Charlie recovers the key, a restored Sam and Dean arrive.
Later, the Winchesters chain Crowley to his chair within the circle and tell him to keep writing down names. They then go to the garage to talk with Dorothy and Charlie. Dorothy is preparing to leave and Sam gives her a copy of her father's book. When she says that it's strange to be a character in someone else's story, Sam says that he understands and that they have to write their own stories. Meanwhile, Charlie talks privately to Dean, thanking him for bringing her back from the dead even though she doesn't know how he did it. Dean assures her that there are no side effects and asks her not to mention it again.
Dorothy thanks them for everything and asks if Charlie is coming to Oz with her to fight against the evil ruler. When Dean warns her that there are unknown dangers, Charlie is happy to hear it and hugs the brothers. Dorothy uses the key to create a portal and she and Charlie head off down the yellow brick road. When Dean wonders if Charlie will ever come back, Sam figures that she will because there's no place like home.