An old man, Mr. Pendleton, drives to an underpass beneath a crossroads and buries a case. A demon, Crowley, appears and Pendleton notes that he was previously negotiating with a young lady. Crowley informs Pendleton that he's a valuable client and then says he'll have to accept a kiss to seal the deal and bailout his bank. Pendleton reluctantly agrees. They're unaware that Castiel is watching them and calls to let Sam and Dean know the deal is going down. As Crowley teleports away, Castiel follows him to a nearby home, warded in Enochian runes. Dean tells him they'll take it from there.
That night, Crowley sips a drink and watches World War II footage of Nazis. Jo arrives at the gates and says that her car broke down. Two security guards come out and tell her to come in. When she tries to leave, their eyes turn black and they grab her, but Jo dispatches them with the demon-killing knife and Sam arrives.
In his room Crowley smiles as the power goes out. He goes to check and finds Sam and Dean waiting for him. Crowley notes it took them long enough and notices the rug between them is askew. Lifting the corner, he sees they've painted a devil's snare on the backside, and chastises them for ruining his very expensive bauble. Suddenly a pair of Crowley's demon goons step up from behind, holding Sam and Dean's hands behind them. Crowley
triumphantly brandishes a pistol -- or, the pistol.
Crowley aims at Dean, but shoots the demons instead. Crowley tells them that they need to talk and explains that he distributed rumors to attract them, and now he wants them to use The Colt to destroy Lucifer. He explains that Lucifer is an angel who hates humans, and he hates demons even more. Lucifer created demons as cannon fodder, and will destroy them once the humans are gone. Crowley just wants things to go back to normal. He extends the gun to Sam, who takes it and asks where the Devil is. Crowley tells him he can be found in Carthage, Missouri. Sam then points the gun at Crowley and pulls the trigger, but discovers it's unloaded. Dean wonders if he's considered all the options, including what happens if they fail, and Crowley tells them that he's taking an extended vacation, and they shouldn't miss.
Back at Bobby's house, Ellen and Castiel are having a drinking contest while Sam wonders if the whole thing is a trap. Dean figures they have to take a chance no matter what, and determines that Carthage is heavy with Revelation omens, with six people missing. However, he tells Sam that he has to stay behind so Lucifer has no chance of getting hold of his chosen vessel. Sam insists that they have to do it together. Dean reluctantly gives in. They notice the drinking contest and Dean goes over to hit on Jo and try his "last night on Earth" speech. She starts to kiss him, and then tells him that she'd rather keep her self-respect. Bobby calls them over for a group photo and Castiel warns them it really will be their last night on Earth. Their smiles fade, resulting in a grim photograph.
The team drives into Carthage, where the street are empty and their cell phones have no service. Dean and Sam go to the police station while Jo, Ellen, and Castiel try to find someone on the streets. Castiel realizes that the town isn't empty and focuses, seeing that there are hundreds of Reapers only he can view. He warns that they only assemble in times of great catastrophe, and tells Jo and Ellen he's going to find out why they're here. Castiel leaves them, and notices one moving in an upstairs apartment. He teleports to the location and follows the man further into the building. A light flares and someone says "Hello, brother."
Jo and Ellen check with Sam and Dean and tell them that Castiel went after the Reapers.
Castiel finds himself in a circle of burning holy oil. Lucifer is there and is well aware that Castiel came with the Winchesters. Castiel notes that Lucifer's vessel is deteriorating and Lucifer admits that "Nick" is wearing a bit thin. Then the angel insists he won't get Sam's body, and Lucifer notes that they are both rebels that were cast out. Castiel refuses to join forces with him.
The others search the town and find Meg waiting for them. When Dean aims the Colt at her, invisible hell hounds start moving in. Meg invites them to come to see her father but Dean shoots one of the hell hounds with The Colt and they run. Dean is taken down and Jo comes to his aid, but another one attacks and rips open her stomach. Dean picks her up and they take refuge in a shop and salt the doors and windows. Dean tries to rig a radio and call Bobby. They get hold of him and update him on the situation. Dean warns that Jo isn't going to survive and starts to crack, but Bobby helps get it under control. They then confirm there were over a dozen Reapers and Bobby concludes that Lucifer is going to use a ritual to unleash Death, the Fourth Horseman. He has also been researching Carthage, and informs them that the Angel of Death must be freed on a place of major carnage. As it turns out, one such place is Carthage, where a major civil war battle took place on the land known as William Jasper's farm.
Meg arrives to tell Lucifer that she has the Winchesters pinned down. Lucifer tells her to leave them alone for now and, when she protests, he explains that everything happens for a reason. Castiel listens, and notices a heating pipe overhead. Lucifer says they have time to see if he can change Castiel's mind.
Dean and Sam try to figure a way to transport Jo, but she tells them that she can't be moved. She suggests that they build a makeshift bomb of nails, salt and propane, so she can draw in the hell hounds while the others slip out. Ellen refuses to let Jo sacrifice herself but Jo asks her to treat her like an adult for what will probably be the last time. Ellen cries and then tells them to go to work.
The brothers assembles a bomb using propane and nails. Dean gives Jo the trigger and says they'll meet again on the other side. He kisses her on the forehead, then on the lips. Ellen kneels next to her daughter and Jo realizes that she's staying to let the hell hounds in. She tells Jo that it's important, and tells Dean and Sam to get going. As they leave, she tells Dean to kick Lucifer in the ass, and "don't miss." Once they're gone, she turns on the propane, unlocks the doors, and breaks the salt lines. She tells Jo that she'll always love her, and then realizes that her daughter is dead. The hounds snarl and enter, but Ellen can't see them. She can only hear them drawing closer, until one billows her hair with its breath. She grimaces angrily. "You can go straight back to hell, you ugly bitch."
Outside, the Winchesters are barely down the fire escape in a nearby alley as the hardware store explodes in a fireball.
Dean and Sam make their way through the woods to the farm and find the mesmerized townsfolk. After figuring they've said everything they need to, they step out and confront Lucifer. Lucifer assures Sam that he'd never hurt him, and Dean gets behind him and shoots him in the head. Nothing happens for a minute, and then Lucifer winces in pain and gets back up, and asks where they found the Colt. He then casually smashes Dean against a tree, heals the wound, and continues his conversation with Sam. He explains that there are five things that the Colt won't kill, and he's one of them. He continues digging while Sam checks on Dean, and then asks if Sam would just agree. Sam insists it will never happen, but Lucifer tells him it'll happen within six months, in Detroit. Sam gets angry and says he'll kill him himself, and Lucifer encourages him to give in to his rage. He explains that most of the townspeople have demons in them, and the women and children are dead and sacrificed to Death. Lucifer insists that he has to do what he's doing and says Sam should understand. He explains that he was a younger brother who loved and idolized his older brother. Michael turned on him and called him a freak, and beat Lucifer down for being different. He asks Sam if that sounds familiar.
Lucifer begins his chant to summon Death and has the other demons recite along with him. The demons collapse and Lucifer casually dismisses their sacrifice.
Castiel concentrates and slowly unfastens the bolts holding the heating pipe with his mind. Meg boasts that her side is going to win. Castiel tells her that Crowley believes Lucifer will destroy the demons once he has achieved his goal, but Meg doesn't believe it. As she moves closer, Castiel finally loosens the pipe and it knocks her into the circle. He tries to exorcise her, but nothing happens and Meg boasts that he's cut off from Heaven. When she asks what he can do, he throws her into the oil, breaking the circle, and walks to freedom over her body.
The ground starts to shake as Death is freed. Castiel appears and gestures the brothers to be quiet. Lucifer steps to the edge of the pit and greets Death. Castiel teleports the boys to safety.
Dean and Sam get back to Bobby's house and they listen to the reports of death and destruction near Carthage. Bobby tosses the photo into the fire and the three of them watch as it burns, Sam staring at Dean's face, and Dean staring at Jo's.