The Book of Kings is the book that replaced the Book of The Wild, sometime around the early 2000s.
The Book of The Wild was the term The Monarchs used for the time before everything changed. Some unknown individual changed the Book of The Wild and in its place was The Book of Kings. This individual edited out the Book of Briars and all magiq after that.
The changes were complex, in the way the one imagine a book and then someone decided to edit that book to remove something fundamental. Stories would have to be changed, characters rewritten, outcomes altered and the ripples of all those changes would extend into the future chapters and the past. It would be impossible to catch all the hanging threads. Scattered memories would be missed… and wells. Wells in the Book of Kings were like hidden themes that remain, despite the narrative being altered.
The Book of Kings was first mentioned in Mr. Wideawake. Mr. Wideawake explained to Deirdre Green the names for the time periods that the Monarchs had created, and the fact that the timeline had been altered by an unknown entity.
The Book of Kings was again mentioned in "Wonder" when Saberlane discovered the Ackerly Green Secret Society pins. Knowing that Ackerly Green Publishing was a failure in the Book of Kings, he surmised that the pins must have been an untouched relic from the Book of the Wild.