Mary is descended from Albrecht van Closen through his descendant Elsa von Closen, who moved to England and in 1920 married Michael Keay. The couple had a daughter, Mary Keay, in 1924. (Whether this is the Mary Keay is unclear, as in MAG 62, Mary states she was 9 years old in 1955.)
Sometime before 1955, her father committed suicide by slitting his throat with a straight razor, which was left to Mary. Mary claims this was the only good thing he ever did for his family. (MAG 62) Mary's mother worked part time for the Magnus Institute, which did not pay well enough to support the family; she also worked at a factory on Globe street to make ends meet. In her spare time, she instructed Mary on her "true studies," and young Mary spent much of her time scouring secondhand and antique shops for paranormal artefacts.
In 1955, Mary started watching Dr. Margaret Tellison, a doctor who lived near her and had her practice in her house, noticing that she seemed to have an aura of power around her. Eventually she saw the doctor murder an unnamed patient and write on their skin; later, she saw her reading from a book made of human skin and summon a spirit trapped within to ask them for their financial information. Mary was offended seeing that the doctor was only using her power to make money. Soon after, she committed her first murder, slitting the doctor's throat. She admits to Gertrude that she enjoyed watching the doctor commit the murder more than she enjoyed performing a kill herself. Mary stole the two paranormal books the doctor kept in her safe, the one made of human skin and used to trap spirits, and one full of poems about dying animals written in Sanskrit.
She spent the next several years mastering the skin book, and learned Sanskrit.
Her son, Gerard Keay, was born at some point in the 1980s, as he was in his late teens in or not long before 2002. (MAG 35) His father was Eric Delano, who worked in the Archives of The Magnus Institute. (MAG 154) He was murdered by Mary not long after their son's birth. (MAG 111)
At some point, Mary opened 'Pinhole Books,' a shop in Morden, London that specialized in rare and antique books. Gerard referred to this as her "day job"; she also had another "vocation" that involved the supernatural and meeting with supernatural creatures. Both jobs required frequent travel.
Jurgen Leitner first visited Pinhole Books in 1993. He is known to have purchased several books from Mary, including the dead animal poem book.
Sometime in 2008 she was found dead of a supposed overdose; although she had been partially flayed. Pieces of her skin were hanging nearby, covered in Sanskrit. Gerard was tried for her murder, but he was acquitted when an important piece of evidence was ruled inadmissible.
As explained by Gerard in MAG 111, Mary's death was self-inflicted, as she died while attempting to complete a ritual to take control of the skin book. After Gerard's arrest, Mary manifested and somehow removed the book from the evidence lockup, while contaminating all the rest of the evidence against Gerard. Through this ritual, she was able to project herself into the world, and "continue her work."
Pinhole Books closed officially after her death.
In 2012, Dominic Swain came into possession of the book Ex Altiora. Eventually he found Pinhole Books, which was staffed by an old woman, with a shaved head and sporting numerous tattoos of words all over her body. (MAG 4)