The 39 Clues by Gordon Korman, Jude Watson, and others

Amy and Dan Cahill never had a normal moment in their lives. It didn't help when their grandmother died and left them one of the most strangest wills in the history of wills. They can either take one million dollars or go on a hunt for world power in the form of 39 clues.Surprisingly, Amy and Dan choose to go on the hunt for the clues... all 39 of them. But they are facing horrible danger. The other teams hunting for the 39 clues will do anything to get them... wether it means alliances or well... let's just say they will do ANYTHING to get the clues.