Throughout the hunt for the 39 clues, Amy and Dan Cahill have uncovered history's greatest mysteries and their family s deadliest secrets. But are they ready to face the truth about the Cahills and the key to their unmatched power? After a whirlwind race that's taken them across five continents, Amy and Dan face the most the difficult challenge yet-a task no Cahill dared to imagine. When faced with a choice that could change the future of the world, can two kids succeed where 500 years worth of famous ancestors failed?