Beverly Tanner is the mother of Duane Tanner.
Sam is having another foreboding nightmare as the episode begins. In the dream, Dean is aiming his gun at a young man who's tied to a chair, repeatedly screaming It's not in me!!, and begging for his life. Dean seems to hesitate, but tells him that he's got no choice. As he pulls the trigger, Sam wakes up on the floor beside his bed.
Sam and Dean travel to River Grove, Oregon, per the clues in Sam's dream, and manage to find an address for the young man they think might be the subject of the dream, Duane Tanner.
Sam and Dean arrive at the Tanner residence. Duane's brother, and then his father answer the door and tell them that Duane is away on a fishing trip. Alerted by their creepy demeanor, the guys duck back toward the back of the house instead of leaving. Through the window they see that the two of them have Mrs. Tanner bound and gagged. She's cut and bleeding and Mr. Tanner is using a butcher knife to cut his son's arm. He purposely drips his blood into the wound on his mother's arm as the guys break the door down, guns drawn. Mr. Tanner charges them with the knife, and they open fire. the son escapes.
They take Mrs. Tanner to the town clinic. She tells the doctor that her husband and her son Jake beat her and tied her up. They were normal one minute, she says, and then "they had the devil in them." Sam and Dean have an aside and discuss the possibility of mass possession. All communication is down in River Grove. Dean decides that Sam will stay there while he drives to the next town for help.
Dr.Lee examines a sample of Mr. Tanner's blood under the microscope. She determines that his body was fighting off a viral infection and that the virus seems to have left a weird residue that appears to be sulfur. As Sam looks on, Dr. Lee tries to explain the infection to Beverly, and asks her if she remembers having any contact with her husband's or Jake's blood during the attack. Beverly seems confused but agrees to let the doctor take a blood sample. Suddenly, she violently grabs the doctor's wrist and strikes her in the face, screeching. She throws Sam across the room into a cabinet and then starts to come at him with a sharp instrument. He quickly recovers and knocks her out with a fire extinguisher.
Dean returns with the Sarge, whom he encountered after having been prevented from getting to the next town by a group of armed men blocking the road, Jake Tanner among them. Sam tells him about the doc's findings and some notes on the word "Croatoan" that he found in John's journal. They realize that the townspeople may be infecting each other with this demonic virus through blood to blood contact.
Sarge alerts them that they need to take care of Beverly because she's been infected. He witnessed what happened to his neighbors; they became so strong he had to kill in self-defense. He insists that the longer they wait, the stronger she'll get. They cautiously enter the utility room where she's been locked down, guns drawn. She pleads with Mark, whom she's known all his life, trying to convince him that she's not infected. Mark cannot bring himself to shoot her, so Dean, after verifying with Sam that she's definitely "one of them," steps in front of Mark and fires three shots with steely resolve.
- The actor who portrayed Mrs. Tanner, Chilton Crane, also played Mary Lew in the Season 8 episode Southern Comfort.