The 39 Clues has more than 14 million
copies in print and over 2 million
registered users of the online game
worldwide.
The 39 Clues series centers around the Cahills—the
most powerful family the world has ever known. But
the source of the family's power has been lost. Grace
Cahill, the last matriarch of the Cahills, changed her
will minutes before she died, leaving her descendants
an impossible decision: receive a million dollars or a
clue.