Rick, a truck driver for a cannery, is refueling when a young girl, eve, approaches him. She asks for a ride and Rick agrees. Once they're in the cab, she kisses him and Rick pushes her away and tells her that Jesus is what she needs. She explains that God abandoned mankind, but a mother would never do that. Eve offers to tell Rick a secret and then lunges forward and presses her mouth to his ear as he screams in pain.
Later, Rick arrives home and enters his bedroom. His wife wakes up and smiles, and he beats her to death with a hammer.
The Winchesters meet with Bobby, who has been receiving monster sightings. They track them down I-80 to a town where a man bashed in his family's heads. The three of them pose as FBI agents and talk to Rick, who says that he has no memory of what happened until he woke up at the Starlite Cannery where he works. He called home and found his family dead. the last thing he remembers is giving a girl a ride from the truck stop. Outside, Sam checks the truck stop security footage and spots Eve. On the camera, her face turns into a rotting visage. Bobby suspects that it's the Mother of All, and Bobby says that if they run into her, they need to run. The police get a report of a man going berserk at a cannery and Bobby goes with them while the brothers finish up at the station.
At the cannery, Bobby confirms that one of the workers went berserk and killed six men with a hunting rifle. Bobby is surprised to learn that Rufus is there, posing as a FBI agent as well. He informs Bobby that the shooter is dead, and suggests they partner up. Rufus agrees, but refuses to let him drive. They go to the morgue and examine the shooter's body, and find a piece of black goo in his ear that neither one of them can identify. Bobby figures that both men were connected to the cannery.
That night, Rufus and Bobby meet Sam and Dean at the cannery. They enter the building and find two people: Samuel and Gwen. Dean prepares to shoot Samuel, but Sam stops him. Samuel explains that they're working, and Dean snaps at him. Sam gets him outside and says that they can wait until later to kill their grandfather, after they learn what he knows. When Sam returns, Samuel realizes that Sam has his soul back and doesn't remember what happened while it was gone. Samuel then explains that he and Gwen are hunting Eve, the Mother of All Monsters. When Bobby comments that Dean told him that Samuel threw the brothers to the ghouls, Gwen reacts in shock. Samuel denies it but Bobby tells her to talk to Dean. She goes to find Dean and asks for the truth, and then admits that she didn't know. Dean then takes out a gun and shoots her in the chest. By the time the others get out there, they realize that Dean has fled.
Rufus and Bobby try to save Gwen without success. Rufus and Samuel move the body and return to help Bobby and Sam look for Dean. As Sam goes, he warns Samuel that if he shoots Dean, Sam will kill him. As they search, Sam calls Dean's cell phone. It goes off and Rufus and Samuel spot him. They draw on each other, and Dean insists that he's no longer possessed. Sam and Bobby arrive and they explain what he did when he was possessed. Rufus checks Dean's ear and finds black goo, meaning he was possessed. Bobby says they have to all give up their guns in case the worm is still in one of them. Without the guns, it'll be harder for the creature to kill them. The others reluctantly agree and they lock their weapons in a locker, Samuel going last.
Once the guns are put away, Bobby and Rufus call their hunter contacts, while Samuel goes to the restroom. Once he goes, Sam and Dean follow him. Rufus and Bobby compare notes and realize they haven't come up with anything, and Bobby suggests they go with a frontal assault. Rufus notes that's what happened in Omaha, and Bobby says it's low of him to bring it up.
Dean and Sam confront Samuel about how he turned them over to Crowley. Samuel says that he did what he did, and he's not going to apologize. When Sam doesn't buy it, Samuel offers to tell him what he did that was so much worse. Sam wants to hear it, but Dean ends the conversation and tells Dean that once they've killed the monster, Samuel is next. As Samuel turns away, Dean notices black goo in his ear and grabs him as he goes for a hidden backup gun. As the brothers chase after him, Rufus and Bobby go to get their guns. The brothers lose Samuel and return to get their weapon. The four men start searching, the lights go out, and Sam spots a booby trap just in time. They continue on but a door closes, sealing Sam off from the others. He tries to find a way around and spots Samuel. Samuel walks toward him and appeals to Sam as one of the family. He offers to tell Sam what he did when his soul was gone and keeps coming, and Sam shoots him dead.
The others come running at the sound of gunshots, and Bobby tells Sam to put the gun down. Rufus handcuffs him and has Sam confirm that nothing came out of Samuel's ear. They take him to the mess area and find no sign of black goo. Rufus and Bobby go to get some surgical cars from Bobby's car and get the power up, while Sam and Dean each other and the corpse. Once they're alone, Dean tells Sam that he did the right thing. Sam wonders what Mary would have said, and Dean figures she would have said that you've got to earn the right to be family. Bobby and Rufus get the power up and return with a cranial saw. Bobby tells them to take a break so they don't have to watch Samuel's skull get split open. The brothers go outside and Rufus plugs the saw in. Bobby admits that Omaha was his fault and says that he's sorry, but Rufus tells him that it won't change a thing and he'll never forgive him for what happened. He then starts cutting into Samuel's skull... and the corpse opens its eyes. It knocks down Rufus and Bobby and then bars the door. While Rufus tries to take the corpse down, Bobby grabs him and throws him onto the electrical outlet. The shock causes the slug to emerge from Samuel's body and it scurries away.
Dean and Sam break into the room and check their friends. They figure that electricity is the creature's weakness, but realize that they've lost track of the again. Dean figures it's in Bobby or Rufus, but Rufus notes that the brothers weren't watching each other 100% of the time. The group checks that there's no goo in their ears, but realize the monster might be covering its tracks. Sam says there's one way to check and strips the wires on Bobby's cranial saw. He tests the corpse first, and then Dean and Sam check themselves. Rufus refuses, saying he has a pacemaker, but finally give sin. That leaves Bobby, who backs away for moment... and then stabs Rufus in the chest.
After a brief struggle, the brothers outnumber the possessed Bobby, knock him out, and tie him up. They wake him up and shock him, and the creature talks through Bobby saying it's comfy inside of him. It invites them to ask whatever they want, and says that Eve has newly created it. Eve is the Mother of All, and plans to breed enough monsters to outnumber humanity. The creature led the brothers to the cannery to tell them that Eve is pissed and there'll be nothing but pain for them from now on. Dean tortures Bobby's body with electricity, and Sam wonders how much more their friend can take. When the creature says they can't kill it without killing Bobby, Dean and Sam both agree to do what Bobby would want. They gag Bobby's body and apply the electricity. After a long few seconds, the dead slug falls out of Bobby's ear and the brothers realize that Bobby isn't breathing.
Later, the brothers meet at a gravesite... and Bobby joins them. He explains that when his wife was possessed, it was Rufus that exorcised the demon and then covered up the fact that Bobby stabbed her. They worked together until Omaha, and Rufus never let it go. Dean says it doesn't matter, and that their lives are too short to hang onto grudges. Sam notes that he's done a lot of crap, but Dean forgives him for all of it. Bobby pours a bottle of scotch onto Rufus' grave and then drinks a toast to his friend.