39 Clues: Black Book of Buried Secrets

The ultimate guide to the New York Times bestselling series, with an introduction by Rick Riordan!
This book is the ultimate source of all Cahill knowledge. It contains every buried secret, Cahill weapon or gadget, all the strongholds, and each agent and founder. In it, you will discover the true story of Madeleine Cahill as well as what happened after Isabel Kabra was charged with murder. Nothing has been held back.
Seven Cahill agents came together to bring you this book, betraying their branches and their most deeply held beliefs. They did it because there is an enemy approaching far more powerful than the Cahills. Keep this black book close at all times, and be ready.