|After sacrificing a virgin, the Mother of All has finally begun to walk the Earth. Apparently, she's been stirring up some trouble off-screen. She asks a trucker at a gas station for a ride, and he gladly gives her one. Or at least, he tries to. When the trucker asks her name, she simply responds, "Eve". Eve in mythology is the first wife of Adam. She begins to come on to the truck driver, and when he pushes her away, she gets angry. He suggests that she 'find Jesus'. Eve leans over to whisper a secret, and suddenly she seems to latch on to his ear. She's in fact depositing what looks like a 12 inch harpy inside his ear, which makes him kill his whole family with a hammer.
Back at Bobby's, Sam and Dean find a link in a series of monster attacks they think were made by Eve, leading them back to the truck driver. After questioning the truck driver, they find out that it IS Eve causing all this trouble by looking at a traffic cam footage. Another attack happens while they're busy in the station, and Bobby decides to take up the job. After finding a man who had gone berserk with a rifle, and was struck dead, he bumps into his old friend Rufus. They both examine the body, and see a black goo coming out of his ear. After close observation, they rule out ectoplasm, giving them no leads as to what it could be. Rufus teams up with Sam, Dean, and Bobby and the four of them head up to the cannery to try and figure out what's going on.
Of course, there's a problem. Somebody else is already snooping around, and it just happens to be Samuel - Sam and Dean's grandfather - and Gwen. Sam, back when he was soulless, had teamed up with them both before, but that doesn't stop him and Dean from having a negative reaction upon seeing Samuel there. Dean is having a harder time controling himself, and Sam eventually has to lead him out of the room, telling him that he can shoot Samuel later, but right now they need to figure out what's going on. As this is happening, Samuel accuses Bobby of trying to be the boys' father. Bobby retaliates, saying that 'somebody 'ought to'. Gwen is confused as to why Dean had that reaction, and, when told the story, she goes to try to make peace with him, disgusted with Samuel. Samuel is telling Bobby, Rufus, and Sam that he believes Eve is over 10,000 years old, and that every monster can be traced back to her.
Meanwhile, Gwen is talking to Dean. She's telling him how she didn't know, and Dean seems to forgive her. Then he pulls out his gun and shoots her in the stomach, leaving the audience confused as to whether this is revenge or if he was hoisting a twelve-foot harpy in his ear.
After hearing the gunshot, the rest of the team run out to discover Gwen dead, a bullet-wound in the stomach. When they find Dean, he tries telling them that he didn't shoot Gwen, that he woke up to see a twelve-inch worm crawling out of his ear and that's it. Samuel clearly doesn't believe him, and even Sam is a bit cautious. After final reassurences, the night begins to turn into a cat and mouse game. The night only gets tenser as they get locked in. Samuel and the boy's won't be working out their problems and it seems like Bobby and Rufus have some problems of their own. When Samuel gets up to go to the bathroom, Sam and Dean follow him. When Samuel becomes cornered by them, Dean is especially testy, and states that when the job is over, he was going to put a bullet straight through Samuel's head. Samuel doesn't apologize for selling them out to Crowley, he says that what he did wasn't half as bad as what Sam did during his 'summer vacation'. After seeing Sam's face, and Dean's realization that the wall could very easily break, Dean tells Samuel to shut up. At that moment a black goo starts to leak down Samuel's ear, and he pulls out a back-up piece. Everybody else is scrambling around for the guns they had discarded just in case.
They all go looking for Samuel, trying to stay with each other and keeping a look out for where ever the goo-harpy monster could be slithering. Sam becomes seperated from the rest of them, and has to go the long way around to meet up with them. As he's moving, he spots Samuel and confronts him. Samuel starts to taunt his grandson, saying that he could tell him everything if he'd just put the gun down. Ignoring Sam's protests of 'stay where you are', Samuel treads even closer to Sam, and without hesitation or even flinching, Sam shoots him straight in the head. Apparently, Sam didn't want to find out what he had been doing soulless with Samuel and his band of family Hunters. When the others get there, the first reaction is relief at seeing Sam alive and unharmed. The second reaction, is thinking that Sam was infected with Eve's creation. Sam tries to deny it, but in the end allows them to tie him up. Guilt is written on his face as the truth of what he did started to sink in, which is even worse when Rufus and Bobby can't find any black goo in Samuel's ear. Sam is upset, questioning that he shot Samuel when the monster wasn't even inside of him. Rufus and Bobby leave to get the cranium saw out of Bobby's truck. Bobby tries to apologize for something that happened in Omaha (it's not made clear exactly what, but Bobby struck a nerve for Rufus), and Samuel suddenly shoots up. Alive.
They taser him with a live electrical wire, and Samuel's dead again - the harpy inside of him seems to be strongly affected by electricity.
The only logical conclusion to see where the harpy went off to, is to shock everybody in the room and see who reacts the strongest. Everybody is clear, but when it comes to Bobby, he backs up, making him look extremely suspicious. When Rufus tries to attempt to shock Bobby, he gets stabbed in the heart. After initial shock, the boys manage to tie Bobby down and ductape him to a chair. After electrocuting "Bobby", the harpy finally tells them that he was sent with a message for the Winchesters: "Winchesters, you will feel more pain from this day forth, pain like you haven't felt before." Apparently, Dean doesn't seem to agree with this, and electrocutes "Bobby" so hard it seems like Bobby's heart won't be able to beat any longer.
The next scene is of the boys standing over a grave, which we assume is Bobby's, but then Bobby comes up behind them, excluding that idea. They came to pay their last respects to Rufus. Bobby is about to admit to whatever happened in Omaha, but Dean cuts him off, saying that life is too short and bloody for them to linger on past deeds. Bobby looks slightly relieved but conflicted, as though he wanted to get it off his chest but at the same time keep it a secret. It ends with Bobby pouring scotch over Rufus' grave.