The Black Grimoire is a powerful spellbook filled with druidic magic.
The Loughlin Family was a family of powerful witches who once owned the Black Grimoire. Aspiring or talented witches would come from around the world to study the Black Grimoire's secrets for a price. When hunters attacked the family, three members managed to escape and took the Black Grimoire with them. The surviving three Loughlin's eventually settled in Eureka Springs, Arkansas.
In 2017, the Loughlin Family drew in the attention of Sam and Dean Winchester after they killed Barry Gilman for stealing money from them. Dean personally hunted down and killed Gideon Loughlin, but not before Gideon cast the Memory Curse on Dean. When Sam discovered Dean was gradually losing his memories and his identity, Sam employed Rowena to help cure Dean. They were unfortunately captured by the two remaining Loughlins', Catriona and Boyd, but Dean killed them using witch-killing bullets, rendering the Loughlin Family extinct. Rowena was then able to use the Black Grimoire to break the curse Gideon had cast on Dean.
Although Rowena intended to take the Black Grimoire with her, Sam confiscated the book but agreed that he and Dean owed her one for her help.
In 2018, Rowena MacLeod plotted with Jamie and Jennie Plum to steal the Black Grimoire. While Rowena sought a ritual within it that could remove the Grand Coven's binding upon her and restore her full powers, the Plum sisters wanted to use the book to resurrect their dead mother. The Plum sisters were able to use a love spell to get Dean Winchester to steal the book for them, but were betrayed by Rowena who had cast a tracking spell upon the Black Grimoire.
Unable to correctly read the Black Grimoire, the Plum sisters' attempt to resurrect their mother went awry, bringing her back as a zombie that was magic-proof. Though Rowena offered to help bring Mrs. Plum back properly in exchange for the book, the sisters sent their zombified mother to attack Rowena who was helpless as she could not harm Mrs. Plum with magic. In the fight that followed, Rowena killed Mrs. Plum with Dean's gun and forced the Plum sisters to kill each other using the Attack Dog Spell.
In the aftermath, the Black Grimoire was recovered by the Winchesters who once again refused to allow Rowena to take the book. However, sympathetic to Rowena's situation, Sam provided her with the page from the book that contained the ritual that Rowena needed as later discovered by Dean. That night, Rowena performed the ritual detailed on the page from the Black Grimoire and regained her full powers.
Months later, Rowena began searching through the Black Grimoire for a way to keep a rift open for the Winchesters once Lucifer was no longer powering the ritual used to open the rift. As time ran out thirty-one hours later, Rowena used the Black Grimoire to perform a spell to augment the power of the rift, keeping it open for a much-needed few minutes longer before it finally closed.
Although it is named the Black Grimoire, the tome itself has a dark green leather cover. It has a silvery heptagram symbol adorned on its cover, and smaller one on its side cover. Like all old books, it has aging papers.
The book itself was written in Old Gaelic text. Among its contents, it features a set of tables of Druidic glyphs and pictures which provided detailed steps for spellcasting. The book's spells include the Memory Curse and its reversal, a soul switching spell, a resurrection spell that if done improperly will result in the person coming back as a zombie and a ritual to remove a magical binding from a witch. The book contains a spell that can be used to augment the power of a rift between universes and keep it open a short time longer by channeling power from the book itself to act as a power source.
- The Black Grimoire is the second powerful spellbook sought by both the Winchesters and Rowena MacLeod for their own purposes with the first being the Book of the Damned. Unlike with the Book of the Damned, the Winchesters have managed to hang onto the Black Grimoire with Rowena not putting up much of a fight over the book.
- In Various & Sundry Villains, its shown that the Winchesters keep the Black Grimoire in the bottom drawer of the card catalogue in the library of the Men of Letters bunker.