Mary was descended from one of the oldest families in Tennessee and took great pride in that fact. She married a doctor, with whom she had a son named Eddie. However, her upbringing of Eddie was strict and overbearing. In 2003, her husband died, and sometime later, Eddie moved to Boston to attend college. In attempts to continue controlling him, Mary called him three times a day and at one point, traveled to his college campus to break him up with a girlfriend she disapproved of. As a result, Eddie rebelled and partied excessively, winding up addicted to drugs like cocaine and methamphetamine. He later suffered a psychotic break brought by the drugs and was institutionalized for six months in 2005. Ashamed of her son, Mary cut off all contact with him. After six months, unbeknownst to her, Eddie checked himself out and went back home following a failed attempt to contact her. Upon arrival, he started a killing spree, guided by his mental imbalance and psychosis.
After abducting a boy named Wally Brisbane and brutally murdering his grandmother, Eddie takes him to the Mays home and approaches Mary, telling her he brought her an angel. Though horrified by her son's actions, Mary wanted to protect him and her family name, and so, she removed all of the evidence Eddie had left in the house, bleached the inside of the refrigerator, wiped away the blood, and hid Wally in a secluded storage shed. After Eddie is arrested by Elle and Morgan, Mary, feigning innocence, assists in his interrogation, signs his medical release forms and allows authorities to give him anti-psychotics. After Eddie's hospitalization, Wally is found by Hotch and Elle, who realized Mary knew where Wally was after discovering that she had cleaned up after Eddie; they look at the GPS device in her car, which shows that she had visited the same secluded area six times in two hours. After helping the police find the storage shed where Wally was held, Mary was likely incarcerated as she is shown being led away by an officer.
- December 14, 2005: Wally Brisbane (held captive; was rescued the next day)