The New York Times bestselling series. On the hunt for the 39 Clues, Amy and Dan Cahill uncovered shocking information about their past - from what happened the night their parents died to the shattering discovery about their family branch. But the biggest secret of all remains behind Grace Cahill s alternate will. Now, Amy and Dan are about to discover a long-hidden secret of the Cahills - a secret so dangerous that people died to protect it. Will this be the end of them? Or just the end of everything they think they know?