Missouri is a psychic practicing in Lawrence, Kansas. She is listed in the phone directory there. John first meets Missouri on December 17, 1983. (See The Journal) Dean and Sam are led to Missouri when they are in Lawrence by the line in John's journal: "I went to Missouri and found the truth."
Following a vision Sam has, the boys return to their home in Lawrence, Kansas. They visit Missouri Mosely, who recognizes them without introduction, and also knows of Jess’ death and John’s disappearance. 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, and he and Dean sit in the car watching the house. Suddenly Jenny appears, screaming at the upstairs window, just as she did in Sam’s dream. The boys rush inside and Dean takes Jenny to safety. As something attacks him, Sam gives Ritchie to Sari and they run outside. 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 who commands 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 her 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.
Missouri features in the Supernatural comic book tie-in, Origins. Origins is set in the era of Dean and Sam's childhood, while John was becoming a hunter.