|“||It was not a book—not with paper and leather.
It had been formed of dark metal plates bound on three rings of gold, silver, and bronze, each word carved with painstaking precision, in an alphabet I could not recognize.
The Book was said to have been created using the last of the molten ore used to forge the Cauldron, formed of dark metal plates bound on three rings of gold, silver, and bronze. The Book is written in the Leshon Hakodesh, it contains spells to negate the Cauldron's power or to control it wholly.
Before there were courts in Prythian there was a Cauldron, from which all things arose. A race of faeries from another world feared the use that could be made of the power of the Cauldron and so they created a Book with the secret to counteract its powers, written in the Holy Language, Leshon Hakodesh.
So that the Book would not fall into the hands of someone who tried to destroy it, the Fae split it into two pieces, one was kept in the Summer Court and the other was given to the Mortal Queens, who protected it and the Book could not be stolen with magic, it had to be given of their own free will.
This was part of the Treaty, but purely symbolic, because the Cauldron had been lost for millennia and was considered a mere myth. The Book was believed to be harmless because like calls to like, and only that which was Made can speak the spells in the Book and summon its power. No creature born of the earth can wield it, so the High Lords and humans dismissed it as little more than a historical heirloom.
After Feyre Archeron defeats Amarantha in Under the Mountain, the Attor disappears taking the remains of Jurian and heads to Hybern to place himself under the command of the King of Hybern. He plans to use the powers of the Cauldron to resurrect Jurian to help him conquer the Mortal Lands again, but for that he has to make the Cauldron whole by gathering its three feet.
Upon learning that the King is in search of the three feet and has already obtained two, Rhysand, the High Lord of the Night Court and Feyre pay a visit to the Bone Carver in the Prison and he tells them what the King can do, and that the Book can nullify the powers of the Cauldron. Knowing this, Rhysand sends a request to the Summer Court to pay them a visit and when it is accepted he travels to Adriata with Feyre and his Second-in-Command Amren.
Once there, Feyre is able to trace half the Book to a temple that is most of the time submerged by the ocean, and using the powers she obtained from Tarquin, the High Lord of the Summer Court, when she was Made, she is able to enter the temple ruins and take half the Book, but not before it realizes she is not Tarquin and tries to drown her.
Back at the Night Court, they discover that the Book is written in Leshon Hakodesh, an ancient language that only Amren can read. Days later their request to meet with the six mortal queens is accepted by the latter.
Five of the six queens attend the meeting as apparently the sixth is ill. The meeting takes place at the Archeron's Estate between the queens and the delegation of Fae comprised of Rhysand, Feyre, Cassian, Azriel and Morrigan.
The queens refuse to give their part of the Book as they have heard rumors about Rhysand's personality and his court and say that they will think about it only if he proves that those rumors are false. After having a little discussion with Nesta Archeron they leave.
Some time later they meet again with the Fae, but this time only two of them attend. Rhysand shows them through the Veritas the truth about Velaris and tells them that the rumors of cruelty are propagated by himself to protect his city and its inhabitants. The queens are grateful for his trust but still say they have to think about whether to deliver half the Book or not. Before leaving, one of the queens, the oldest, shows them a letter sent to them by Rhysand saying that she loves Feyre and wants a better world where she can visit her sisters without facing hatred. After that they leave but under the chair of the other queen they find the other half of the Book that she has brought them since she read the letter and also wants a better world. She asks them not to say that she had given it to them, since if they find out they could kill her as they did with the sixth queen, who they had said was sick when she is not.
After bringing the two parts together, Amren is not able to decipher the spell to nullify the Cauldron's power, and tells Feyre not to unite the two halves as it would be felt by faeries around the world. When they are in Hybern to render the Cauldron powerless, Feyre listens to what the two parts of the Book tell her and thinking that only in that way can they nullify the power of the Cauldron she unites them and that causes the King to detect their presence and catch them. When they manage to flee the kingdom, Rhysand takes both parts of the Book, much to the King's displeasure.
Later Amren studies the Book endlessly to obtain the key that would allow them to nullify the power from the Cauldron but without success.
When Feyre meets with the Suriel he tells her that the answer Amren was looking for was on the second page and the penultimate of the Book, but it is not the key to nullify the power of the Cauldron but to release her from her Fae body, which she did with the help of Feyre and when she frees herself the Cauldron breaks into three parts, leaving a void coming out of it that consumes everything. Looking for a way to contain it Feyre takes the Book looking for a spell but not understanding the language, throws the Book into the void out of frustration and the Book is not seen again.