A Clue found in Book 3 sends Amy and Dan jetting off to find out just what's behind the fierce rivalry between the Tomas and Ekaterina branches of the Cahill family. Was a Clue stolen from the Tomas branch? Where is it now? And most important, can Amy and Dan get their hands on it before their rivals do?

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,...

When Amy and Dan learn the truth about the Madrigals and Grace Cahill's alternate will, these discoveries lead to the revelation of a secret about their family and a showdown with the man in black who has been following them.

Guardians of the 39 Clues, Dan Cahill and his sister Amy discover that the serum is missing and must race against time to get it back before catastrophe strikes

Shaken by a shocking loss, Amy and Dan flee to an exotic land and trace the footsteps of their most formidable ancestor yet: a military leader of mythic proportions.

Amy and Dan Cahill travel to Australia to figure out what their own parents knew about the object of their quest, but their search brings back terrible memories for Amy and endangers a secret ally.

Amy and Dan Cahill have their final confrontation with twisted billionaire J. Rutherford Pierce, a man whose power has no limits and is one step away from being elected president.

Amy and Dan are in a race for their lives . . . and the enemy may be even closer than they think. When seven members of their family were kidnapped by a sinister organization known as the Vespers, thirteen-year-old Dan Cahill and his older sister, Amy, vowed they'd stop at nothing to bring the hostages home. But then the ransom comes in and the Vespers demand the impossible. Amy and Dan have just days to track down and steal an ancient map. The only...

Returned by a surprising twist to their first mission on U.S. soil since the beginning of the Clue hunt, Amy and Dan discover evidence of a mole in their organization who proves to be one of their closest confidantes and who reveals, even more disturbingly, the true agenda of the Vespers.

The Cahills are the world's most powerful family, but their strength is being tested. A sinister man calling himself The Outcast has targeted the family and set them an impossible test. He's recreating four of history's worst disasters and challenging the young Cahills to find and stop the tragedies before it's too late. Now, with one disaster behind them, siblings Dan and Amy Cahill and their friends have just days to discover what the Outcast's...