Maeve O'Farrell was an Irish witch and occultist who worshiped The Outsider, a figurehead and puppet of a Great Old One. Her grimoire is a written collection of all of her esoteric and occult knowledge, which includes a variety of spells. Upon Maeve's death in 1918, the grimoire was passed on to her younger daughter, Moira O'Farrell-Havelock. The grimoire is written in an Irish replacement cipher and is guarded by Maeve's former familiar, an ageless sphynx tomcat known as Oghma who can see into the space between worlds.
Following Moira's ownership and additions to the book, the grimoire is passed on to her magically-inclined middle child, Matthias Havelock.