|As spoken in Latin||English Translation|
|Exorcizamus te, omnis immundus spiritus...
hanc animam redintegra...
|We exorcise you, every impure spirit...|
Fix this soul...
A demon is a human soul, twisted and corrupted by its time in Hell. Father Thompson believed that you could wash that taint away and restore their humanity.
The ritual must be performed over consecrated ground. The person performing the ritual can use either their own purified blood (after going to confessional) or sanctified blood (donated blood blessed by a priest). One universal symptom of both renditions of the cure is that the demon may experience pain while undergoing the injections as seen with Peter Kent and Dean Winchester.
Purified blood must be injected into the demon every hour for eight hours. As the ritual progresses, the demon may begin expressing human emotions in the process. After the eighth dose is administered, the following exorcism must be recited:
Exorcizamus te, omnis immundus spiritus
hanc animam redintegra
lustra! (slice your hand and place it over the demon's mouth)
After this, the demon will become human once more.
The use of sanctified blood does not require the exorcism to be recited nor does it affect Dean's demonic mannerisms, even though the cure progresses with turning him back to human enough to remove the warded handcuffs and walk across the devil's trap in the Bunker's dungeon. Only when the final dose is administered does his behavior return to normal.
Looking through the Men of Letters Bunker's archives, Sam and Dean find a film where two priests, Father Max Thompson and Father Simon try a different type of exorcism on a possessed old woman. The result is that the woman's chest is burst open. Talking to the Father Simon, they discover that Father Thompson believed it was possible to cure a demon and turn them human again and the ritual was being used to that effect but failed. Listening to a recording of the last attempt Father Thompson made two days before he died, Sam and Dean learn that he finally succeeded by, on consecrated ground, injecting a demon with his own blood, purified by confession, over a period of eight hours until the demon began to sound human then performed the exorcism while putting his bloody hand over the demon's mouth. The demon became human again.
Sam and Dean set out to try the cure on Abaddon, but she escapes when they are distracted by Crowley calling to threaten to kill all of the people they have ever saved if they don't hand over the demon tablet and back down from the trials. He also starts keeping all demons away from the Winchesters as he has realized they may need one for the third trial and with no Abaddon, Sam and Dean are left without a demon to cure.
After Crowley starts killing all the people they have saved, Sam and Dean pretend to make a deal with him. At the ruins of Singer Salvage Yard, Sam shows Crowley the demon tablet to prove he has it while Crowley shows them the angel tablet. Crowley produces a contract many yards long, and Dean insists on reading the fine detail. As he does, he gets close to Crowley and snaps handcuffs on him connecting him to Dean. Crowley is initially amused until they reveal that they have carved a binding spell on them, keeping Crowley trapped and powerless. Sam and Dean take Crowley to a small church to undergo the third Trial - curing him.
Soon Castiel arrives, telling Dean he needs his help in undertaking the Heaven trials. Dean is reluctant to go, but Sam insists he will be fine. After confessing his sins, Sam starts injecting Crowley with his blood. After each injection, Sam's arms start glowing for a short period of time. At one point Crowley bites Sam, and when he leaves to get a bandage, Crowley casts a spell and uses the blood to send a call for help. Abaddon arrives, and throws Sam through a window, but she tells Crowley she is not there to help him, but to take over ruling Hell. But Sam douses her meatsuit with holy oil, setting her on fire. Abaddon is left in such pain she abandons her body and flees the scene. Crowley starts regaining his humanity and tries to bond with Sam, tearfully declaring that he deserves to loved and wonders how he could even begin to ask for forgiveness for his actions. Sam suggests he start by going along with the cure and he willingly allows Sam to give him the next injection.
Dean arrives just after Sam performs the exorcism and is about to complete the ritual by slapping his bloody hand over Crowley's mouth and begs him to stop warning it will kill him after finding out from Naomi that God wanted the person doing the Trials to make the ultimate sacrifice to complete them. Sam initially wants to keep going, feeling he has let his brother down too much, but Dean convinces him to stop and Sam lets the Trials go, causing the glowing that had appeared in his arms to disappear. However, he collapses soon afterwards due to the fatal damage that had already been done to his body.
After tracking down Dean, Sam offers to cure him, reminding him that they can do that, but Dean claims he doesn't want to be cured and that if he did, he would've stuck around for Sam to do it.
Having captured Dean, Sam attempts the cure on him even though he's not sure it will work with the Mark of Cain. To this end, he has a priest bless a roomful of blood and then consecrates the devil's trap in the Men of Letters Bunker with holy water. Sam starts injecting Dean with the sanctified blood which causes him great pain. However, Dean retains demon mannerisms long into the ritual and taunts Sam about what he did to try to find him.
The ritual eventually makes Dean so human that he is able to escape from the binding link handcuffs and devil's trap and tries to kill Sam. Castiel recaptures him and Sam finishes the ritual. Dean's black eyes disappear and he is now unaffected by holy water, proving that the cure had worked.