Grace is the last matriarch of the Cahills, the world's most powerful family. Everyone from Marie Curie to Harry Houdini is related to the Cahills, yet the source of the family's power is lost. 39 Clues hidden around the world will reveal the family's secret, but no one has been able to assemble them. Now the clues race is on, and siblings Amy and Dan must decide what's important: hunting clues or uncovering what really happened to their parents.