The 39 clues. Unstoppable

When an enemy finds a way to use the source of the Cahill family's power against them, siblings Dan and Amy embark on a desperate mission that will take them from one extreme of the Earth to another, but Dan may have to face the one terror he never imagined--betrayal by his own sister.

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.