This is the first book in the "39 Clues" series by Scholastic. Amy and Dan, orphaned children being raised by a very distant great aunt by way of au pair, are sent on a wild hunt around the world for clues following the passing of their wealthy maternal grandmother. She was some sort of archaeologist/explorer, and has set up this elaborate scheme for her kin following her death. By following the 39 clues, they will discover some grand secret which will change the world.
The family breaks into teams to see who can discover the secret first. Dan and Amy discover that their family has some very famous members. In this volume, they discover they are related to Ben Franklin and follow in his footsteps from Philadelphia to Paris. At the end of the book, after they have discovered a clue from Franklin, they are moving on to discover more about Mozart, another one of their relatives.
While I found the writing uninspired, the mystery component kept me reading. Upper elementary students would enjoy the adventures of two kids and their au pair on their own against teams of adults and other children in this quest. There are scary moments, as some of their distant relatives are "evil" and try to eliminate the competition by attempting to kill Dan and Amy. There are plenty of educational opportunities for kids as they read, and it just might whet their appetites to learn more about the historical figures they encounter.
There are apparently going to be 10 books in the series, and they are releasing book 7 or 8 now. There also is an online component, where a child can play along and could possibly win $100,000. It's no Westing Game, but I recommend it and look forward to following the clues along with my children.