Jenny has just moved into a new house in Lawrence, Kansas with her two children Sari and Richie, having moved from Wichita after either leaving her husband or her husband's death. She settles Sari into bed. Her young daughter is nervous in the new house, but Jenny reassures her that there is nothing scary in her closet.

Jenny continues her unpacking, until a noise draws her down to the basement, where she discovers a trunk full of old photos. One shows a family, and is inscribed on the back “The Winchesters. John, Mary, Dean, and Little Sammy.” Upstairs, Sari screams as the closet door swings open, revealing a figure made of flames.

Sam wakes up from a dream of Jenny, screaming from Sari’s bedroom window.

Dean is researching new cases, but Sam is distracted as he sits, obsessively sketching the image of a tree. Finally he pulls out an old photo from his duffle, and recognizes the tree as the one that grew outside their childhood home in Lawrence.

Sam tells Dean he has dreamed of something bad happening at their old house. Dean is skeptical as to why they should return to Kansas based on a dream, but Sam reveals he dreamed of Jessica’s death, just the way it happened, several days before the actual event.

Dean is disquieted by returning to the family home. When they arrive, Sam explains to Jenny that they used to live there, and she shows them around. She explains the strange occurrences – the flickering lights, noises, and the being Sari reported seeing.

After they leave, Sam and Dean decide they need to approach this like any other case and research the past of the house. They compare notes on what John has told them of the night their mother died, and Dean relates what he remembers from the night. Sam is surprised; he never knew Dean carried him from the house.

When he has a moment alone, Dean tearfully calls John asking for his help, and reveals how upset he is over the whole situation.

Back at the house, Jenny has called in a plumber after the garbage disposal has stopped working. As he tries to fix it, a toy monkey mysteriously starts banging its cymbals, and the unit starts up, tearing apart the man’s hand.

The boys a go to a garage and speak to Mike Guenther who co-owned a garage with John. He reminisces about the time after Mary’s death, and mentions that John visited every psychic in town.

As Sam searches through he telephone book for psychics, a name rings a bell with Dean - Missouri Mosely. The first sentence in John’s journal reads: “I went to Missouri and I learned the truth”.

The boys visit Missouri Mosely who recognizes them without introduction, and also knows of Jess’ death and John’s disappearance.

Meanwhile, something has helped little Ritchie escape from his playpen, and then traps him inside the refrigerator, although Jenny rescues him.

Sam, Dean, and Missouri return to the house and explain to Jenny that they can help rid the house of whatever is there. Missouri senses two presences, one of which is a mean poltergeist, but neither of which were responsible for Mary’s death.

Missouri has the boys help her prepare bags filled with ingredients that will help purify the house. As they start placing the bags, the poltergeist fights back violently, trying to stop them. Finally all the bags are placed, the house appears peaceful, and Missouri declares the house safe.

Sam is less sure, so he and Dean sit in the car watching the house. Suddenly Jenny appears, screaming out the upstairs window, just as she did in Sam’s dream. The boys rush inside and Dean takes Jenny to safety while Sam gets the children. As something attacks them, Sam gives Ritchie to Sari and they run outside, but the front door slams shut behind them.

Dean breaks down the front door, and finds Sam in the nursery, where some force has pinned him to the wall. Just then a fiery figure appears, but just before Dean shoots it, it coalesces into the figure of their mother, Mary.

She acknowledges Dean, and says “I’m sorry” to Sam, before commanding the poltergeist to leave the house, and disappearing herself in a ball of flame.

Jenny and her family return to the house, and promises to keep an eye on them, as Sam and Dean take their leave.

At home, Missouri, muses that she is surprised, that given his powers, Sam couldn’t sense the presence of his father - John Winchester is in her sitting room. Missouri tells him to go and see his sons, but he says he can’t until he knows the truth.

Information from Supernatural Wiki