After beginning a war to take control of Hell from Crowley, the Knight of Hell Abaddon began ramping up production on her demon factories across the country, having the demons in charge steal souls from people so she could turn them into a demon army loyal only to her. One of these demon factories was in Milton, Illinois where Abaddon had once battled Henry Winchester and Josie Sands as they attempted to stop what they thought to be a simple case of demonic possession. This factory was led by Abaddon's old minion Sister Agnes and another demon possessing a local man named Mr. Richie.
Hunter Sam Winchester catches wind of one of the factory's victims, Karen Young, brutally murdering her husband and decides to check it out, believing it to be a case of demonic possession. His brother Dean refuses as he has grown obsessed with finding and killing Abaddon. Sam travels to Milton where the sheriff tells him he didn't notice any sulfur or notice Karen's eyes looking weird and they find that Karen has committed suicide. Sam is left confused by Karen's actions, especially as he finds no sulfur or EMF, but decides to give it until morning before considering it a case of a woman going crazy and leaving.
That night, Sam visits a local diner where Sister Agnes and Mr. Richie's latest victim Billy visits and attacks a waitress when she makes him angry. Sam subdues the young man and finds that along with Billy, three other people have also been affected and are locked up at the sheriff's station. Sam shakes holy water on Billy who is unaffected and tells Sam that he's doing what he is just because he can and he wants to. Sam notices that the people are acting aggressive, violent and impulsive, seemingly on basic instinct with anything being able to set them off. Sam realizes that the people are acting like he did when he was soulless, except more out of control. Sam asks Dean for help, but Dean refuses, claiming he's too close to finding Abaddon to come.
While studying survelience photos of the grocery store Karen Young visited shortly before killing her husband, Sam overhears a woman named Julia Wilkinson telling a cop that "those demons are back" and that something is happening again. Sam pulls Julia aside and asks her what she knows about the demons. Julia realizes that Sam believes her and asks if he's one of the Men of Letters as they had come to Milton in 1958. Julia explains that the two members of the order that showed up gave false names but she eventually learned their first names were Henry and Josie. Sam is shocked to realize the two were his grandfather Henry Winchester and Abaddon's current vessel Josie Sands. Julia explains that one of the nuns, Sister Mary Catherine had killed two people before committing suicide and Henry and Josie were there to investigate it. Julia tells Sam of how the two believed they were dealing with a simple case of demonic possession, but found the crest for the Knights of Hell. Julia further explains to Sam how she was taken with other victims by the demons that night before Henry and Josie intervened and exorcised two of the demons before being confronted by Abaddon who learned they were from the Men of Letters and possessed Josie to study and destroy the order. Julia tells Sam she doesn't know what Abaddon was up to at St. Bonaventure in 1958, but that it seems to be starting again. In one of the pictures the sheriff gave him from the grocery store, Sam sees a St. Bonaventure van parked next to Karen Young's car and realizes that the demons are once again using St. Bonaventure as their base. Sam is able to get the location of the convent which has been closed for years from Julia.
Now knowing where the demons are hiding out, Sam goes to St. Bonaventure Convent where he locates the stolen souls in the basement. As Sam goes to examine the souls, the demon possessing Mr. Richie attacks him, but Sam quickly kills him with the demon-killing knife. Moments later, Sister Agnes attacks Sam, flinging him into a stack of boxes and taking the demon-killing knife from him. Sister Agnes tells Sam that if he opens the jars holding the souls, he will release them and they will return to their owners which she can't allow. Sister Agnes explains that Abaddon is stealing souls to transform them into demons to help her win rule over Hell. The demon army she creates out of the stolen souls will be unbeatable and loyal only to Abaddon. Sister Agnes tells Sam that Abaddon has demon factories all over and she intends to steal Sam's soul so he will join it. Unarmed, Sam starts an exorcism, but Sister Agnes grabs him by the throat, stopping him. In response, Sam starts a recorded exorcism on his phone and throws the phone across the room. As the exorcism starts to affect her, Sister Agnes desperately lets go of Sam and crawls across the floor towards the phone. Sister Agnes manages to destroy the phone in time to stop the exorcism, but Sam retrieves the demon-killing knife while she's distracted with the exorcism and stabs Sister Agnes in the back, killing her.
With Mr. Richie and Sister Agnes dead, Sam goes back to the jars containing the stolen souls. Sam releases the souls and they return to their owners, restoring them to normal.
The next day, Sam asks Julia why she never warned Henry about Abaddon's possession of Josie. Julia explains how Abaddon threatened her and unsure of how to act in the face of true evil, she gave in and allowed her fear to rule her. Julia had soon after left the convent, ashamed of her actions. Sam reminds Julia that the information she shared with him saved lives and he couldn't have stopped the demons without her. Upon returning to the bunker, Sam joins Dean in attempting to find Abaddon as soon as possible, finally understanding the magnitude of the threat Abaddon poses. Sam and Dean spread the word about the factories to other hunters who see signs of the other factories all over, though no sign of Abaddon herself.
- Sam using a recorded exorcism against Sister Agnes is similar to the method he and Dean used to defeat the demon invasion during Jus In Bello. Unlike there, the exorcism doesn't stop the demon but instead acts as a distraction.
- One of Sam's few solo hunts and fights with demons.
- During the final battle with Abaddon, a similar situation happens to Dean as happened to Sam here: Dean is attacked by a minor demon minion and quickly dispatches them only to be surprised by the real enemy.
- While Dean was able to single-handedly fight and kill three demons while hunting the First Blade, Sam struggles to defeat a single minor demon on his own, relying on a recorded exorcism when unarmed while Dean fought the demons hand-to-hand until he retrieved his weapon.