In Lawrence, Kansas, Jenny is looking at a photo of herself and her husband, when her daughter Sairie comes in and complains that there's a monster in her closet. Jenny checks and assures her that there's nothing there. She then puts Sairie to bed and assures her that the three of them, including Sairie's brother Ritchie, will all be happy there despite Sairie's misgivings. As Jenny goes, her daughter asks her to prop the chair in front of the closet doorknobs.
Downstairs, Jenny starts is unpacking when she hears a noise. She hears something moving in the basement and goes downstairs to investigate. The lights don't work.
Upstairs, Sairie jerks awake as an unseen force moves the door aside.
Jenny finds a metal box. Inside it are various mementoes, including photos of John Winchester and his family.
The closet doors open and Sairie stares as a burst of flame materializes.
Sam dreams of a blonde woman, pounding on the window of their home. The next morning, a distracted Sam does a sketch of the tree he saw in his dream, and finally confirms that it's the tree in their family photo. He tells Dean that they have to go home to Lawrence. When Dean demands to know how Sam knows, Sam reluctantly admits that he's been having nightmares, and they're just like ones he saw that predicted Jessica's death. Dean admits that he swore he'd never go back there after their mother died, but Sam insists they have to check it out to be sure. After a moment's hesitation, Dean agrees.
The brothers drive to Lawrence and go to their old home. Dean starts to make up a cover story, but Sam tells Jenny the truth and asks if they can see the old place. She tells them about the photos that she found and invites them in. She introduces them to her children, Sairie and Sairie's younger brother Ritchie, who is in his crib. Jenny explains that the house has issues: flickering lights and rats in the basement. Dean confirms that she hasn't seen any actual rats to account for the scratching noises, and Sairie says she saw a flaming figure in her closet.
Outside, Sam confirms that Jenny was the woman he saw. He figures that the thing that killed Mary and Jessica may be in the house, and they have to get Jenny and her family out of the house. Dean warns that Jenny won't believe them, and they figure they have to dig into the history of the house. Sam notes that they don't know much about the house, and Dean talks about what happened, and how John never shared any of his theories with him. They figure they should talk to the friends and neighbors, same as always, but they both admit it's not a normal job. Dean goes to the bathroom but calls and leaves a message for John on his answering machine, begging him to come and help.
Jenny calls in a plumber, Joe, to take a look at her backed-up sink. She leaves him alone and he goes to work. As he unfastens the trap, a toy monkey starts playing its cymbals on its own. Joe ignores it and cleans out the trap, and then unplugs the garbage disposal. The monkey stops playing, and Joe throws the switch to make sure the disposal is off. He then reaches down to find the obstruction, and the disposal starts up while the monkey begins playing again.
Dean and Sam pose as cops and go to see Mr. Guenther, who owned an auto garage with John. Guenther remembers John as stubborn, but in love with Mary. After the fire, John eventually talked about the fire and said that something caused it. However, the authorities dismissed it as an electrical shock. Guenther tried to get John to see help, but he read up on the occult and went to a palm-reader in town. The brothers check the Yellow Pages and one of the names, Missouri Moseley, piques Dean's interest. He checks John's journal and finds a reference to John seeing Missouri.
They go to see Missouri, who is sending away with a client with fake good news. She ushers them into her parlor and takes Sam's hand, and knows about Jessica's death and John's absence. She explains that she's a psychic, but she can't pull facts out of thin air. Missouri explains that John came to her a few days after the fire, and she told him what lurked in the darkness. John took her to the house, and she got a psychic impression of something evil.
At home, Jenny is on the hone dealing with the fact that the plumber is suing her after he lost his hand. She tells Ritchie that she'll be back in a few minutes.
The brothers tell Missouri their suspicions that something is in the house. She says that she's been keeping an eye on the place, and nothing has happened until now. Sam figures that something is starting.
The unseen force in the house opens the door of Ritchie's crib, and then opens the safety lock on the refrigerator. Ritchie climbs in to get his sippy cup, and the door slams shut while the lock closes. Jenny comes back and discovers that Ritchie is gone. She searches around desperately and finally notices milk spilling out of the door. Opening it, she finds Ritchie inside.
Sam and Dean bring Missouri to the house and ask permission to show her the old place. Jenny says it isn't a good time, but Missouri tells her that there's something wrong with the house, and Jenny knows it. Jenny lets them in, and Missouri goes to the nursery where Mary died. She confirms that whatever is haunting the house, it isn't the creature that took her mother. It's a different energy, and there's more than one spirit in the house. The spirits are there because of what happened to the Winchesters, drawn to the psychic infection. The primary spirit is a poltergeist that wants to kill Jenny and her family. Missouri can't identify the second spirit, and Dean vows that no one will die in the house.
Missouri and the brothers put together mojo bags and prepare to put them in the walls at the four compass points, purifying the house and driving out the spirits. They get Jenny and her children out, and Missouri assures her that by the time they come back from a movie, it'll be over.
The trio splits up and starts knocking holes in the walls to plant the bags. The poltergeist slams a dresser into Missouri as she places her bag, and then throws knives at Dean in the kitchen. An electrical cord strangles Sam, preventing him from putting the bag in the wall. Dean gets there and tries to free Sam, but when that fails, he puts the bag in the wall. There's a burst of light as the poltergeist is driven out.
In the aftermath, Missouri confirms that the spirit is gone but Sam isn't so sure. Jenny returns with her children and is dismayed to see all the destruction. The brothers clean up and leave with Missouri, Jenny goes to bed, but it starts to vibrate beneath her.
Sam has Dean park outside the house, insisting he has a bad feeling. He looks up and sees Jenny pounding on the upstairs window, just like in her dream. They run inside as Jenny tries to get out of her bedroom, only to discover the knob is frozen. In her bedroom, Sairie watches as the flaming figure appears in her closet again.
Dean kicks down the door and gets Jenny out, while Sam runs to get Ritchie and Sairie. He gets the girl out past the flaming figure and runs downstairs, and tells Sairie to take her brother outside. Something grabs him and drags him back to the kitchen, while the front door slams shut on its own. Dean grabs a shotgun and an axe from the Impala's trunk and runs to the front door, and then starts hacking it down.
In the kitchen, the poltergeist slams Sam against the wall. The flaming figure walks into the room and advances on him. Dean gets in and prepares to shoot the figure, but Sam says that he knows who it is. The figure grows solid and reveals that it's... Mary Winchester. She smiles at her sons and calls them by name, and then says that she's sorry. Mary then tells the poltergeist to get out of her house. She bursts into flame and dissipates into the building, and the poltergeist disappears for good.
The next morning, Jenny gives Dean the photos from the basement. He thanks her, but she insists that they're his. Missouri checks the house and confirms that it's clean. She explains to Sam that Mary used her spirit to cancel out the poltergeist's energies, all to protect her boys. She then realizes that Sam sensed that the poltergeist was still there, even when she couldn't. Missouri admits that she doesn't know what's happening to him. She tells them not to be strangers and watches as they leave. Missouri then goes home and finds someone waiting for her: John Winchester. She tells him that Sam has powerful abilities, and that Mary's spirit saved the boys. John considers the wedding ring on his finger, and Missouri tells him to talk to his children. He admits that he wants to, but he can't, not until he knows the truth.