Finding the three pieces of the Book of Ra is the main quest of The Throne of Fire. While there is no reference to a definitive Book of Ra in Egyptian mythology, the many aspects of Ra are alluded to, as is Ra changing forms when in different worlds. Riordan merges common myths about Ra’s different parts, using Khnum as Ra in the Underworld, Khepri as Ra as the dawn, and Ra as the god of day, order, and the sun. The Book of Ra allows Sadie and Carter to combine these aspects of Ra so the god may rise and battle against the forces of chaos and Apophis.

The Book of Ra represents the fickle nature of gods. Carter and Sadie know nothing of the book until shortly before the beginning of the novel, when Horus tells Carter about one of the pieces that’s about to be moved from a museum in Brooklyn. Given how Horus and the other gods are not thrilled by Ra’s awakening at the end of the book, it is possible Horus put off telling Carter about the Book of Ra until it became clear there was no choice but to wake him.