This sounds like the coolest series ever!! I'm so excited about how interactive this is, and totally can't wait to get my hands on it for my daughter *and me & my students.* I have a 12 year old's b-day to attend this weekend and I'm thinking of buying him the book and some cards.
Anyway, here's the skinny. It will be a series of 10 books, written by various authors. The first book, The 39 Clues, Book One: The Maze of Bones is written by Rick Riordan (Percy Jackson & the Olympians series!!) Think Webkinz but the cards relate to books instead of stuffed animals. It has an interactive site http://www.the39clues.com/
I found out about this at a Reading Council meeting (Scholastic rep speakers) I attended tonight, and then read this article that totally sparked my interest!
& a little more about it JIC
Article in Publisher's Weekly