Dean is running down the streets in terror as the sound of hellhounds in pursuit echo behind him. He stumbles across a homeless man and warns him to run before "it" kills him… and a small dog walks into view. Dean runs away from it in terror and it happily runs after him.
Rock Ridge, Colorado
Forty-three hours earlier, Dean and Sam impersonate Federal agents and talk to a coroner about Frank O'Brien, a marathon runner who died of a heart attack at the age of 44. There have been two similar deaths and the brothers ask the coroner to do an autopsy. Dean notices a wedding ring outline and Sam notices scratches on the arm that the coroner dismisses as caused when the man fell. However, the coroner doesn't find any blockages of the artery.
The guys meet with the town sheriff, Al Britton, who was friends with Frank. The sheriff insists on cleanliness, constantly washing his hands. He explains that Frank was recently acting jumpy and refused to answer his phone. Outside, the brothers figure something supernatural is involved, and the other victims had similar red scratches. As they walk down the street, Dean sees several teenagers and takes a different route to avoid them. The brothers then talk to Frank's neighbor Mark Hutchins, who says that Frank was freaking out. Mark keep snakes and crocodiles and Dean gets increasingly nervous. Mark explains that Frank got increasingly scared of everything, but in high school he was a bully. He got better over the years after his wife died 20 years ago, but Dean wonders if anyone would have wanted revenge.
That night, Sam gets into the car, startling Dean. Dean has determined that Frank's wife Jessie, a manic-depressive, killed herself and Frank had a perfect alibi. Sam didn't find anything at Frank's place. They drive back to the hotel but Sam notices that Dean is driving the speed limit and obeying turning laws. He then picks up EMF readings from Dean.
The next morning, Sam calls Bobby and returns to the hotel to find Dean in the car with scratch marks. Bobby has confirmed that it's ghost sickness. Some spirits can infect people with a contagious disease, causing them to die of fright. The disease spread from Frank to the two other dead men who were on his softball team, and Dean caught it from the corpse. Sam tells him that he has 24 hours and all the victims were all dicks who used fear as a weapon. To stop the disease, they have to destroy the ghost. The Winchesters figure that Frank's wife is the ghost. Dean finally admits he was in the car because their hotel room is on the fourth floor.
Later in their first floor room, Dean is trying to read up on ghost sickness but starts to hallucinate accusations and insults in the text. He finally breaks the ticking clock and settles back with a beer. Sam returns, revealing he's discovered that Jessie's body was cremated and she couldn't be the ghost. Dean starts to choke on his beer and coughs up a wood chip. Realizing it's a clue, the brothers visit the local lumber mill. Dean refuses to go in but Sam insists so he takes a big swig of alcohol. However, he refuses to carry any weapons and offers to man the flashlight.
Inside, the EMF detector is useless due to Dean's proximity. However, they find Frank's wedding ring and realize he was there. Exploring further, they open a locker and find a cat and Dean screams in terror. They find a badge belonging to a Luther Garland and an article on Frank's wife, along with a sketch of Jessie O'Brien. Dean accidentally sets off the conveyer belts and then spots a man crouched in the corner: Luther. Dean runs off in terror and Luther advances on Sam, who dissipates him with a shotgun blast of salt: Luther is a ghost.
At the station, Sam checks the Garland file while an increasingly drunk Dean hovers nervously in the background. Luther died 20 years ago of "physical trauma" and the deputy, Linus, doesn't know anything about it. Sheriff Britton is out sick and Sam quickly gets Dean out. Once they're gone, Britton calls in and discovers that the Winchesters are investigating Garland. He realizes they know, then starts scrubbing himself, drawing blood. He hears a voice telling him that they know and fearfully points his gun around.
Sam and Dean go to the hospital to see Luther's surviving brother, John. He finally tells them that Luther was a kind man but a big hulking figure that everyone was scared of because of his looks. John admits he failed Luther. Sam shows him the drawing of Jessie: John recognizes her and tells him that Frank killed Luther. Jessie was a receptionist at the mill and Luther had a crush on him. When Jessie went missing, Frank suspected Luther and went to the lumber mill where he beat Luther then dragged him behind his truck by a chain around his neck until he was ripped apart. John tried to get community pillar Frank arrested but they refused to investigate the murder of the "town freak."
The brothers figure that the scratches are road rash from Luther being dragged to death, and he swallowed the wood chips during Frank's beating. However, Sam warns that they can't burn all the remains given how Luther was ripped up. Dean loses it, saying they must be nuts to hunt monsters. He quits and starts walking away… and hears a dog behind him. The cute dog chases after him…
Dean ends up back at the hotel with less than four hours left. Sam tells him he's going back to Hell and it's about time. Sam's eyes glow yellow and he says that he's going to become a demon. He pins Dean to the wall and then starts choking him. It's a hallucination, and Sam manages to calm Dean down for the moment. He calls in Bobby, who has found a Japanese book on spirits, including a buruburu that infects its victims with fear. It has to be killed like a traditional ghost, but it can also be destroyed using fear. Sam calls Dean to tell him they've got a plan and Dean should just relax and ride it out.
Sam and Bobby go into the lumber mill as Luther watches them. At the hotel, Dean starts to hallucinate hellhounds again, trying to break in. However, it's Sheriff Britton, who demands to know why they're investigating Luther's death. Britton is overcome by fear but defends Frank, his friend, who he refused to arrest for Luther's death. Dean manages to knock the gun away from him and they struggle until Dean manages to throw Britton off of him. Britton cowers back in fear and then dies of a heart attack.
Luther doesn't come out so Sam starts ripping up the pictures of Jessie. The mill machinery starts up and Luther grabs Sam. Meanwhile, Dean continues to hallucinate as the road rash scratches continue to grow. He picks up a Bible… and then sees Lilith appear on the bed next to him. She tells him it's time for him to come back to Hell and asks if he remembers all the "fun" they had there. Dean's heart starts to burst and Lilith tells him he's going to die. He wonders why he got infected and she tells him to listen to his heart.
At the mill, Sam tries to get to his shotgun but Luther yanks him away. However, Sam manages to grab a chain and wraps it around Luther's neck. He yells to Bobby to pull away and Bobby drives around, towing Luther by the chain. The ghost is destroyed, and Dean snaps out of his fear, the scratches gone.
Later, the guys are sharing beers and Sam explains the chain was made out of iron and etched with a spell word. Dean's back to his old self and Bobby heads out. Once he's gone, Sam asks what his brother saw and Dean shrugs and says it was howler monkeys and the other usual stuff: nothing he couldn't handle.