|Location||Mason City, Iowa|
|Episode(s)||12.04 American Nightmare|
Gail Peterson was the wife of Abraham Peterson and mother to Elijah and Magda Peterson. Prior to moving to Mason City, Iowa Gail was severely injured in a car wreck, which was caused by her daughter's burgeoning psychic abilities. Believing the Devil to be inside Magda, the Peterson's moved from the city to the outskirts of Mason City, believing that God told her to live a life of simplicity after her accident. The Peterson's would fake Magda's death and keep her locked away in the basement, where Gail would attempt to exorcise the evil from her daughter as she self-flagellated.
Meeting with Sam and Dean, believing them to be from Child Services, she converses with Sam about God while Dean helps Abraham outside. When Sam notes the happy family picture of the Peterson's, Gail corrects him and explains why they moved out to the country, telling him of her car accident and how God told her to go and live a life of simplicity and modesty. When Sam brings up the death of their delivery boy, Ricky Copeland, he notice's Gail is not surprised by the news, with Gail telling him God has a pan for everyone. When he brings up Magda's death being apart of "God's plan", Gail is cut off before she can answer him, when Sam begins berating her for letting her daughter die. Blaming Gail, not God for Magda's death as Abraham comes back to the house and tells Sam and Dean they should leave.
After Sam and Dean leave, Gail heads to the basement of the house where she has Magda locked away, asking her about the recent death's. When Magda denies doing anything, Gail slaps her and demands penance, handing Magda a whip to flagellate herself and pray for forgiveness.
Later that night Sam returns to the Peterson home and spies Gail speaking in tongues in the basement while Magda whips herself repeatedly. When Sam is eventually caught, he is brought to the Peterson's dining room and where the family is preparing to have a dinner. Scoffing as Gail serves a stew, she explains that the family has been dealing with Magda's abilities for years, explaining that Magda was the cause of the car accident and tells Sam that by keeping her in hiding, they are protecting everyone else. But Sam's protests of Magda's treatment fall on deaf ears as the family bows their heads in prayer. When Abraham takes the first bite and soon dies, Gail explains that it is the only way they will stay together, ordering Elijah to eat. But before he can, Magda causes the spoon to fall from his hands before using her telekinesis to clear the table of the plates. Gail picks up a knife and comes at Magda, inadvertently stabbing Elijah who jumped in the path to protect his sister. As Gail and Magda struggle with the knife, and as Magda turns the knife towards Gail, Sam pleads with her to stop, telling her she can control. The knife soon stops at Gail's chest and drops to the ground.
The next morning Gail is taken away by the police in handcuffs, telling everyone that her daughter is the Devil, before being placed in a police car. She was likely institutionalized upon her arrest.