The Book of the Black was allegedly written "in preparation of the Blackest Night."
The caretaker of the book was a former Guardian of the Universe. During the "Sinestro Corps War", she was greatly disfigured by the Anti-Monitor and later corrupted by the his evil. In the bowels of the planet Oa, she succumbed to this evil and assumed the name Scar. Scar's insight into the prophecy of the "Blackest Night" was intricately tied to the writings of the Book.
During the breakout of the Sciencells on Oa, the Sinestro Corpswoman Lyssa Drak found the book in the deep bowels of Oa. Almost instantly after she found and began to read it, Scar, whom she had not noticed, imprisoned her within the book.
Holy anachronisms, Batman!
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