Title: The Black Book of Buried Secrets
Series: 39 Clues
Author: Mallory Kass
Introduction by Rick Riordan
ISBN: 9780545285049
Pages: 187 pages
Publisher/Date: Scholastic Inc., c2010.

Within these pages, you will find everything you need to become the ultimate Cahill operative. You will learn the secret locations of branch headquarters around the world–even for the Madrigals. The identities of each branch’s key operatives are revealed. Personnel dossiers have been opened for the first time in Cahill history, so you know exactly who works for which branch and what abilities they have.
You will learn about each branch’s top secret arsenals of weapons and gadgets. Nothing has been held back. Once you read this book, you will have the combined knowledge of all the Cahill branches.
Remember: We are risking everything to put this information in your hands. Learn it well. We are counting on you. (9)

This book is more an encyclopedia than a novel, providing a compendium of information about the founders, agents, tricks and tools, and hot spots for each of the five branches. Scattered throughout are updates about the characters of the 39 Clues series, stories about agents past and present, and multiple clues and messages in secret codes of all sorts. Exchange symbols or letters for other letters, use the International Signal Flags, morse code, and more, some of which readers will recognize from the series. It’s really not necessary to read this book to make sense of the series, and is more like a who’s who of 39 Clues than a continuation of the plot. Still, fans will get a kick out of learning more of the history of the clues hunt and it’s obviously a must buy for libraries with a group of clue hunters. Readers can flip through and focus on the people or things that interest them.