A clue sends Amy and Dan jetting off to find out just whats 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? Its a wild race that will take Amy and Dan deep into the bowels of the earth and right into the hands of the enemy.