The Book of the Dead is a grimoire, a magical text, containing all the lore of necromancy and counter-necromancy collected by the line of the Abhorsen.
It is bound in pale green leather and held shut by silver clasps which are covered in Charter marks to bind, blind, close and imprison. Only a person with an innate talent for Free Magic and necromancy may open it and only a person with an unsullied Charter Mark may close it again.
The last line of the book is the only one that doesn't change. "Does the walker choose the path, or the path choose the walker?" In another book, the line said "Does the walker choose the path, or the path the walker?"