A young girl, Maddie Berman, is having a tea party with her toy animals and her imaginary friend Sparkle as her parents look on. Her mother Linda finally says that they're ready to go to dinner and Maddie should let them know when she's ready. As the husband rolls his eyes, Maddie says that they're not ready yet. At the door, Mr. Berman complains that they have reservations, but Linda insists that they be patient. Once they leave, Maddie tells Sparkle that they can party forever. A human-sized Sparkle tells Maddie that he'll clean up and she should go with her parents.
Later, Sparkle is reading a book alone when someone comes in. The imaginary friend leaps to his feet and then stares in surprise, and the newcomer stabs him in the chest. Maddie comes back to her room from dinner and screams at what she sees.
Sam wakes up in the bunker and leaves, unaware that a figure is watching him from the shadows. He staggers down the hall and the figure follows him, unseen. Sam goes to the kitchen and makes himself some coffee, and notices that the table is set with candy and cake. The figure comes up behind Sam and yells "Surprise." Sam punches him and the figure says that he's Sully, his best friend when Sam was a child. Shocked, Sam says that Sully isn't real, just as Dean comes in and sees his brother clutching thin air. He wonders what's going on, and wonders if Sam is having a stroke. Sully explains that Dean can't see him unless he wants him to. He makes himself appear and explains that he made the food appear. Sam explains that Sully is his imaginary friend, and Sully says that someone killed his friend. He explains that he and the victim were Zanna: good guys that help kids. Sam tries to take it all in, and Sully asks for their help as hunters. Dean tells Sam that they're going to talk privately and orders Sully to stay in the kitchen.
In the library, Sam explains that Sully was the only one who knew his childhood desires. He gets out a tome and finds a reference to Zanna: creatures that guide and protect lost children. They appear as an imaginary friend to let the children move on once guidance is no longer necessary. Sam figures that since Sully helped him, they should help Sully now.
Sully leads the Winchesters to Maddie's house and explains that he's in management and doesn't get out much. He came to see his friend Sparkle and found the cops there when Maddie's mother called the cops. Sully says that he'll meet them inside and disappears, and the brothers go in dressed as trauma counselors. As they go in, Sam admits that he didn't think Sully was real and he grew out of it. Dean wonders why Sam needed an imaginary friend when he had him.
A 9-year-old Sam is looking up at a ringing phone. Sully tells him to answer it, and Sam finally does. It's Dean, who says that John said no. Sam insists that he can go hunting with them, and Dean sys that maybe he can come next time. He hangs up to join John in the Impala, and Sully tells Sam that they can finally make some bottle rockets.
Linda answers the door and explains that Maddie made up Sparkle and then thought he was dead, and called the police. They talk to the girl and Maddie says that she doesn't want to go into her room because of all of the blood. v takes them in and leaves them to it, and Sully appears, staring in horror. He steps over Sparkle's invisible body and swears them to secrecy. Once they agree, Sully lets them see what he sees: pools of glittery blood and Sparkle's corpse. Sam confirms that Zanna can see other Zanna, but Sully insists that a Zanna could never kill one of their own. Linda comes in, unseeing, and steps in the blood. Sam suggests that Maddie sleep in the spare bedroom, and they suggest that Linda take a long shower with her family.
A young girl, Zoe, is playing in her wading pool and her mermaid Zanna Nicky is with her. Zoe goes to gymnastics with her mother, and Nicky relaxes in the water. Someone comes up behind her and stabs her to death.
The next day, Sully soon summons the Winchesters to the new crime scene when Nicky doesn't check in with the home office. He explains that Zanna share a telepathic link and takes the brothers to the pool. Sully insists on staying strong for Sam, and Sam confirms that Nicky was also stabbed to death. The Zanna says that Nicky's boyfriend Weems is a little clingy, but he's also one of Sully's best friends. Dean figures that it's a lead and starts to leave, but Sully says that they have to do something with his friend's corpse. As he goes to get shovels, Sam remembers.
Sam and Sully are in the motel room playing a game of "Ever Think?" Finally, Sam asks if Sully has ever thought about running away. He admits that he thinks about running away from the hunting life, and Sully suggests that he wants to go to school and make some real friends. One day Sam won't have him, and Sully tells the boy that he can be whatever he wants to be, and he's awesome. The Zanna tells Sam that it's his life and it's up to him, and Sam says that they're going.
Dean buries the mermaid and complains that Sam isn't working. As Sam digs, he looks over at a grief-stricken Sully. Sully is more concerned about Sam, who says that he's fine.
That night, Weems helps his child Fletcher take his sheets out to dry. The Zanna assures Fletcher that mother won't be waking up anytime soon because she's been sleeping. Once Fletcher goes in, Weems hangs up the bedsheets and sees a silhouette on the sheets. A woman stabs him through the hanging sheets. She drives off in a VW Bug and Weems telepathically calls to Sully.
Sully and the Winchesters soon arrive and find blood everywhere. They follow the trail to a shed and go in, and find Weems laying in a corner. His love handle absorbed the blow, and Dean says that Nicky is dead. Weems is surprised that Sam and Dean can see him, and seems surprised when they tell him that Nicky is murdered. Dean asks if anyone would have a problem with them, and Weems describes the killer and her car. Sam tells him to check on the killer while he stays with Weems and Sully. Before they go, Dean asks Weems why kids like him. The Zanna says that he plays air guitar, and demonstrates that he can really play an invisible guitar.
As Dean leaves, Sully goes to get some bandages. Weems realizes that Sam is "the" Sam and is surprised that they're back together. Sam insists that he's helping Sully out, and Weems tells him that he broke Sully's heart.
John calls and tells Sam that he wants him to go on a hunt. Sully is ready to run away, and disappointed to learn that Sam is going. Sam says that he's a Winchester and hunts monsters, and complains that Sully isn't happy for him. Sully warns that he's going down a path he might be better off not following, and says that there are lots of other ways. Sam insists that he wants to be with John and Dean, and angrily says that Sully isn't real. He tells Sully that he doesn't need him anymore and wishes that he could unmake him, and Sully leaves because that's what Sam wants.
Sully returns and bandages his friend, and Weems goes to check on Fletcher. Sam tells Sully that it's awesome how Sully helps everyone, and he feels awful how they left off. He admits that he was a jerk kid, and Sully says that it was all on him. Sully says that Sam going off to hunt was one of his biggest failures because it was clear Sam wanted something else. The Zanna figures that he was wrong and it all worked out, but Sam isn't so sure. Sully assures Sam that he did well, and Sam admits that there was some bad and some really bad. He confesses that he let something out into the world, and Sully knows about the Darkness from rumors. Sam promises to fix it with Dean, but he figures that he can't release Lucifer from the cage in Hell... even though that's what God wants him to do. Sully plays "Ever Think" and asks if Sam has considered running away. Sam says that he hasn't in a while, and his phone rings. It's a text from Dean saying that he's found the killer and tells Sam to come and bring Sully. Sam takes Sully out to hotwire a minivan.
Dean wakes up and the killer puts away his cell phone. She tells Dean that Sam is on the way.
Dean pulls up to the address belonging to the VW Bug and the killer knocks him out from behind.
The killer--a woman named Reese-- steps forward and says that they have a mutual imaginary friend: Sully.
Sam and Sully arrive and find Dean. Reese is holding a knife to his throat, and Sully recognizes the girl. She offers Dean for Sully, and says that Sully killed her sister. Sully insists that it was an accident. He explains that Reese and her twin sister Audrey were his first kids after Sam abandoned him. Sully insists that he was the one who messed things up, and let Audrey sister chase him into the street when they were playing Tag. He didn't see the car, and never went back into the field because he was scared he'd hurt another kid. Reese says that she was bounced from shrink to shrink and no one would believe her when she said her imaginary friend killed Audrey. She studied the folklore and went to Romania, and found out about the Zanna. Reese found a witch who sold her a spell to see the Zanna, and a dagger that would kill them. Now she's going to save other kids by killing the Zanna.
Sully says that he would have called if Reese had called, and Reese says that she liked seeing him suffer. She needed Sully after Audrey died, but he never came back. Sully says that he panicked when Audrey died and he left Reese to deal with the pain because he couldn't handle being the one who caused it. The Zanna says that he does whatever is best for the kids, and offers his life if it will make Reese feel better. Reese steps forward and screams that she's mad and can't stop it.
Dean manages to work through his bonds and tells Reese that revenge won't make her feel better. He says that Sully was there for Sam when he wasn't, and the Zanna are the furthest thing from monsters. Sully says that he's sorry, and Reese drops the dagger and hugs him, crying.
Later, Reese takes off and Sully figures that Sam never wants to see him again now that he knows the truth. Sam says that Sully is a hero to him, and tells the Zanna that heroes aren't perfect. Sully agrees and says that sometimes heroes are scared, but the thing they're facing is super important and nobody else can do it. Dean comes over and Sully says that he'll check in on Reese. He thanks Dean for looking out for Sam, and Dean says that he's a good weird. Sully wishes Sam luck and disappears.
As the Winchesters drive back to the bunker, Sam says that they need to discuss him going into the cage. Dean says that it's not happening and insists that there must be another way. Sam asks him what it is, and Dean doesn't have an answer for him.
Written by Gadfly on Dec 3, 2015