When Ra stopped ceased his nightly journey, the cycle was broken; Ra faded into permanent twilight.
The Book of Ra describes how Ra can be awakened. Ra’s priests created the book in ancient times and kept it secret, dividing it into three parts, to be used only if the world was ending.
The Book of Ra was divided into three sections. It was intentionally divided to make it difficult to find, so only the worthy would succeed.
The first part of this book was found in the Brooklyn Museum. It was hidden in a statue of the god Khnum, who was depicted forming a human out of clay. Its location was disclosed to Carter by the falcon war god Horus in a dream. When picked up, due to a high sensitivity after so long in darkness, it activates every reservoir of magic in the museum including a griffin and seven bau and lights up the whole city with ghostly fires before Bast cast a spell to dial down the sensitivity. This section was used by Sadie Kane to return the ren of Khnum.
The second part of this book was in St. Petersburg. It was hidden in the top drawer of Vlad Menshikov's desk. Its location was disclosed to Sadie by Anubis during a chat in London. This section is used by Sadie Kane to awaken Ra's form as "the noonday sun".
The last part of this book was in Bahariya. It was hidden in a tomb. Its location was disclosed to Sadie by Set in St. Petersburg. This section of the book was used to awaken Khepri, the scarab beetle, but in doing so, releases Apophis. After this section was read, the book of Ra vanished.