After a series of brutal murders, Dean, Sam and Bobby travel to investigate and they meet Rufus. They team-up and find that Eve, a.k.a. The Mother of All, is the responsible for the killings. When they find a clue of the location where she might be, they stumble upon Samuel and Gwen who are also chasing Eve. Soon they learn that Eve has created an evil worm that penetrates through the ear and force the victim to kill. Now they do not know who might have been possessed by the creature.
Sam, Dean and Bobby set out in search of The Mother of All's latest monster. While investigating, they run into Samuel and Gwen, who are also hunting the creature. Samuel and Bobby get into a heated fight about how to handle the case.
- Bobby tells Sam and Dean about the numerous reports of monster activity that he's been getting from other hunters. All of the monsters seem to be springing up along I-80 leading to Sandusky, Ohio, where Rick, a trucker for Starlight Cannery, recently murdered his whole family with a hammer. Bobby, Sam, and Dean go to question the man, but he has no memory of the event. His last memory is of a young woman asking him for a ride at a gas station. At the police station, they watch the footage from the gas station's security camera, and they see the young woman. Static runs across the screen, obscuring most of her face, but what they can see looks like a monster, and Bobby speculates that they're dealing with the "Mother of All." While they are at the police station, a call comes in that a man has gone postal at the Starlight Cannery, and Bobby goes along with the responders while Sam and Dean stay behind. At the cannery, Bobby meets Rufus, who is on the same case, and learns that a worker came to the cannery with a hunting rifle and killed six others before being shot by police. Rufus partners up with him and they go to the morgue, where they examine the man's body. They find black ooze in one of his ears, but it isn't ectoplasm, and they're stumped as to the cause.
They decide to investigate the cannery, and all four men break in at night. There, they encounter Samuel and Gwen Campbell, who are on the same case. Dean wants to kill Samuel, as he promised he would in 6.10 Caged Heat, but Sam persuades him that Samuel might be useful in the hunt. Dean leaves, angry, and Samuel reveals to the others that the case they're on involves the Mother of All, also known as Eve, and that she is the creator of all the monsters they hunt. As they talk, Bobby mentions Samuel's betrayal of Sam and Dean, and Gwen is shocked and leaves to talk to Dean. She tells Dean that she didn't know about Samuel betraying Sam and Dean to Crowley, and Dean shoots her. The others rush into the room and find Gwen dying. They assume that Dean has been infected like the other two men who went postal, and they search for him. When they find Dean, he tells them that something worm-like crawled out of his ear. They dub the creature "the Khan Worm," and together the hunters try and work out a way to find and kill it.
Bobby has them give up their guns and locks them in a locker. When Samuel leaves the room, Sam and Dean follow and confront him about what happened with Crowley, but Samuel is not apologetic. He then pulls an extra gun he had hidden and tries to shoot them, as he is infected with the worm. They stop him and he escapes. Eventually, Sam finds and confronts him alone. Samuel says he will tell Sam about the things he did without a soul, but he advances on Sam and Sam is forced to shoot him. When the others find them, they are uncertain whether the worm was in Samuel or if it is in Sam, so they tie Sam up and resolve to cut open Samuel's head and check for the Khan Worm.
Sam and Dean leave the room and, as Rufus and Bobby prepare to cut open Samuel's skull, they discuss an unfortunate hunt they were on together in Omaha. It can be inferred that Bobby messed up on the hunt and caused the death of someone that Rufus cared for, and Rufus says that he will never forgive Bobby for what happened. When they begin cutting into Samuel's skull, the Khan Worm animates Samuel's dead body and attacks them. During the struggle, Samuel is electrocuted and the worm leaves his body and infects Bobby, who then stabs and kills Rufus while he is possessed.
Sam and Dean overpower Bobby and tie him up. They electrocute him as they question the Khan Worm inside him, and they learn that the worm is a new creation that Eve cooked up to lead them to Sandusky. She has a message for them that the worm relates: "She's pissed, she's here, and it's going to be nothing but pain for you from here on in." Sam and Dean tape over Bobby's ears and electrocute him until the worm slithers out of his ear and dies.
After the creature is killed, Bobby, Sam, and Dean bury Rufus. As cremation is not undertaken in the Jewish tradition, Rufus is buried, in what is obviously a Jewish cemetery, rather than given a Hunter's Funeral Pyre. Bobby pours some of Rufus' favourite drinkJohnny Walker Blue Labelon the grave before taking a drink himself.