The Mary Day case involves the mysterious disappearance of 13-year-old Mary Day from California in June 1981. Mary lived with her biological mother, sister, and an abusive stepfather—whose violent behavior and claims of being "possessed by a demon" after beating Mary led to her disappearance. Following the incident, her family was warned to avoid a specific area of their yard, and decades later, cadaver dogs alerted authorities to that spot, where a small child's shoe was found. Years later, a woman in Arizona claiming to be Mary Day was confirmed via DNA testing as her biological daughter. Despite this identification, lingering doubts remain, and the case continues to be shrouded in mystery and unresolved questions.