The Book of Books was a legendary tome whose pages never ran out, telling an infinitely long story.
It found its way in the 18th century into a cache of books which also included a series of books about the War which originated in another universe where they were but fiction. The books were discovered in the 21st century and transferred to the New York Public Library, where they were set to be unveiled with much pomp, with journalist Rachel Edwards covering the story and interviewing Johannes Englesberg III, a scholar who had not realised the true nature of the Book of Books, being more interested in the other texts and describing the Book as an unimportant "outlier" which "appear[ed] to feature many texts condensed within it" with no clear narrative connection to the rest.
Other parties, however, were much more interested in the Book of Books than in the other texts. They included War powers such as people in robes, people with masks and people in "silver jumpsuits", but also powers from the 10,000 Dawns. The Arbiter of Knives was the first to tell the Arbiter of Eternity about the Book, thinking it would be a way for them both to while away eternity, with the incredibly old Arbiter of Eternity having finished reading through all the books which had ever been published in the 10,000 Dawns. She was overheard by spies from the Great Assimilation and the Dawn organisation, who followed her to the Totality to get to the Book first — in Dawn's case to prevent anyone from stealing it at all, as they feared the consequences if the Firmament-equivalents learned of their trepassing into the Totality.
Arriving on Earth, the interdimensional spies also caught the attention of the Strid, a local alien species who decided to get the Book before anyone and then auction it off to some of the interdimensional parties, desiring a planet of their own where they'd rule themselves and be guaranteed a supply of bodies. After the Arbiter of Knives cut her way through the representatives of the local power, this auction began to take place, with the Firmament and Assimilation each offering the Strid a planet while Dawn refused to negotiate with the murderous beings and simply gave them a flat ultimatum to surrender the book peacefully. In the end, however, Rachel Edwards, whose temporal shadow the visitors were using to cloak their presence, took advantage of this position to win back the book herself, threatening (as a pure bluff) to kill herself and thereby expose them unless the Strid gave her the book. Accepting they'd been beaten, the Strid, Assimilation and Firmament representatives all retreated.
Because it had been tainted by Strid biomass, the Book was taken away from the Library to a secure location, along with the other volumes; the official story was that it had been found to be infected with a long-dormant parasitic fungus, on which the deaths caused by the Arbiter and Strid were blamed. (PROSE: Rachel Survived)