On a lonely road, the radio plays a song as a couple gets lost and have a fight when a man appears on the road. They go off and hit a tree, and when the woman Molly wakes up she finds her husband gone. She finds a house and the man they saw on the road, and he starts to bleed and his guts spew out, then comes at her. She runs back into the woods and onto the road where Dean and Sam just avoid hitting her. She takes them back to her car but it's gone.
They drive her to see the cops when the radio starts up on its own. A voice says "She's mine" and the same man appears on the road. Dean drives right through it and is dissipates, and then the car shuts down. They explain the man is Jonah Greely, a local farmer who died on the highway 15 years ago, and on the anniversary of his death he finds someone to punish. Molly reluctantly accepts their story and takes them to Greely's hunting cabin. They need to find his corpse to salt and burn it, and go out to look. Greely grabs Molly but Dean sends it away with a blast of salt and then they follow a path through the woods to a house.
The three go into the house and search the place, and Molly finds pictures of Greely and his wife, who were in love. Exploring the house, they find the corpse of Greely's wife, who hung herself. Sam insists on burying the body and secretly suggests to Dean that they should tell Molly about her husband. Dean says not to but Molly insists. Before they can say anything, a jukebox starts up with the same song, and the words "She's mine" appear on a window. Another window behind Molly shatters and Greely pulls her out before going into the woods. They check out the photos and spot a tree planted as a grave-marker, and realize that's where the body is.
Greely has Molly tied up and she tries to plead with him but he starts to cut her. Dean sends him away briefly with a rock-salt blast but Greely reforms and knocks him around. Sam digs up the body as Greely grabs a knife and comes at Dean. The two struggle while Sam finds the bones and salts and burns them, and Greely disappears in a burst of flame.
They go back to the Impala but Molly insists on knowing what happened to her husband David. Sam admits that David is alive and says they'll take her to him. They drive up to a house and she sees him alive, and with a new wife. Sam explains that 15 years ago Molly and David hit Greely and he survived… but she didn't. She's been haunting the highway along with Greely. They determined someone was killing people along the highway and talked to David, who revealed Molly's body was cremated. When they drove the road and spotted Molly, they realized she was unaware that she was dead so they played along.
As the sun starts to come up, Molly want to tell David what happened, but they say she has to accept what happened and move on. She does so and disappears in a burst of light as the sun comes up.