Sam goes to a local blood bank and convinces a priest to sanctify the blood. He then goes back to the bunker and into the cell where he has Dean restrained in a devil's trap. Dean tells his brother that he doesn't want to be cured and wonders why Sam cares what he does. Sam prepares a syringe with the blood and Dean warns him that he just won't sit there like Crowley did, and that it was the Mark of Cain that made him a demon. When Dean prepares to struggle, Sam throws holy water in his face and injects him with the blood. As Dean writhes in pain, Sam tells him to stop struggling and make it easier on himself.
As Castiel drives to the bunker with Hannah, she finally admits that it bothers her that Sam has asked Castiel for help. She realizes that Castiel didn't tell Sam about his condition, and Castiel says that it doesn't matter. He warns her that they may have to destroy Dean if the blood cure doesn't work, but Hannah is more concerned about her fellow angel.
Sam continues giving Dean injections, and Dean warns that he could be dying and all of the lore is just crap. When Sam says that he isn't talking to the real Dean and that he's just doing what he can, Dean tells his brother that he knows what he did to find him, and asks which one of them is really the monster.
Sam tracks down Lester Morris at a bar and approaches him. Lester says that he wants to get revenge on his wife for cheating on him, and Sam takes him to a crossroad and shows him how to summon a demon. When Dar arrives, Lester makes a deal with her before Sam can stop her. Sam then captures Dar and tortures her for information on Dean's whereabouts.
Dean tells Sam that the line between him and the monsters they hunt is thinner than his brother thinks, and congratulates Sam on getting Lester killed. Sam administers another injection, sending Dean into spasms of pain. Once he recovers, Dean asks Sam if he has what it takes if the cure doesn't work.
In Hell, Crowley is sentencing the demons that joined Abaddon. His courtier reports that Castiel has lost his grace and is dying, and suggests that they dispose of him. Bored, Crowley thinks back to when he was partying with Dean. A demon interrupts him to say that they all know about Crowley spending time with Dean. He offers to be Crowley's new wingman, and an irritated Crowley destroys him with a snap of his fingers.
The next morning, Hannah becomes lost and they pull over to check the map. When she says that she knows how to restore his grace, Castiel stops her and tries to walk away. Hannah stops him, just as Sam calls. Castiel says that he's on his way and Sam says that the treatments are apparently killing Dean. Castiel warns Sam that the blood ritual is the only way he knows of to cure Dean, and warns his friend that they'll have to kill Dean if they can't cure him.
Dean passes out and Sam slaps him awake. His brother says that he likes what he's become, and tells Sam that he chose Crowley over him because he was tired of babysitting Sam. Sam says that John taught them that Winchesters don't get to quit, and Dean says that their father brainwashed them into fighting his losing battles. Angry, Sam injects Dean with another dose of sanctified blood and steps outside.
In Crowley's throne room, a demon finally rebels, saying that he's had enough of Crowley. He takes out a flask and the other demons fall back, and the rebel demon says that Crowley has been letting Hell go to hell while carousing with Dean. Disgusted, he says that he'd rather die than stay there and sets himself on fire with the holy oil in the flask. Crowley stares at the remains and admits that he didn't see that coming.
Castiel and Hannah stop at a gas station and Castiel obliquely tells his companion that she has to resist temptation. She says that she knows what both of their priorities are and goes inside. Looking around, Hannah finds the clerk dead, his eyes burned out by angel fire. A few minutes later, Castiel finishes pumping the gas and comes in, and finds Adina holding a knife to Hannah's throat. When Castiel tries to draw his knife, he waves and begs Adina to kill him but let Hannah go. The rebel angel throws Hannah into a shelf, stunning her, and then kicks Castiel outside and starts beating him.
While waiting for Dean to recover, Sam goes to his brother's room and looks around. He finds family photos of the Winchesters and looks through them for a moment, and then tosses them on the table and leaves.
After Adina is finished beating him and goes back to Hannah, Castiel looks up and realizes that Crowley is there.
When Sam goes back to Dean's cell, he discovers that his brother has escaped.
Adina cuts Hannah with her blade, insisting that she should have just let her and Daniel go. Crowley comes in and cuts Adina's throat, draining her grace into a receptacle. He then kills her and goes back to Castiel.
Sam avoids his brother in the bunker hallways and gets the keys to the power room from the main room. Meanwhile Dean finds a hammer and yells at Sam to show himself.
Crowley forces the grace on Castiel over the angel's objections, pointing out that Castiel has no choice so his hands are clean. Once he is restored to his angelic power, Castiel heals his wounds and Crowley says that the angel owes him. Castiel wonders why Crowley helped him, and the demon says that he wants him to take care of Dean one way or another. The angel isn't convinced, and Crowley tells him that he's not sentimental and leaves.
Sam goes to the power room and shuts off the generator, locking the bunker down. Dean assures his brother that he has no intention of leaving until he finds and kills Sam. As he goes into the main room searching for his brother, Dean boasts that Sam's treatments only made Dean human enough to pass through the devil's trap and escape the keys. When he realizes that Sam took the keys to the doors, Dean goes to the power room and turns the power back on. Sam, hiding outside, slams the door shut and locks it, and begs Dean to let him finish the cure. Dean starts breaking through the door, yelling that he prefers to be a demon, and is sure that Sam won't be able to kill him.
Dean breaks through the door and goes after Sam, saying that it's time to finish the game. Dean comes up behind Sam and attacks him, and Sam ducks just in time and puts his knife to huis brother's throat. Dean dares him to kill him, saying that it will be Sam's decision. Unable to do it, Sam lowers the knife and as Dean prepares to attack... Castiel grabs him from behind and says that it's over.
Later, Sam gives Dean another injection and tells Castiel what his brother has been saying about wanting to be a demon. Castiel admits that he can see why Dean would feel that way because then he doesn't have to feel pain. Dean wakes up and acts normally, and Sam uses holy water to make sure that he's cured.
Later, Sam approaches Castiel and says that Dean is doing better, and asks the angel to keep an eye on Dean while he goes for a food run. Castiel warns Sam that eventually the Mark of Cain will exert its influence on Dean again, but Sam wants to recover from the last problem before dealing with the next one. Castiel then goes to see Dean, who is in his own room looking at his family photos. Dean realizes that Castiel is a full angel again, and Castiel assures him that Sam knows that not everything that Dean said was from him. Dean thanks his friend for being there for him, and Castiel says that they can all take a break now that Heaven and Hell are back to normal.
In Tulsa, Oklahoma, a human-appearing woman—Rowena—is in her study reading a book. She looks up at the two men that she has pinned to the ceiling with spikes and then goes back to reading.
Written by Gadfly on May 22, 2016