The 39 Clues is a series of adventure novels written by a collaboration of authors. They chronicle the adventures of two siblings, Amy and Dan Cahill, who discover that their family has been, and still is, the most influential family in history and their quest to find the 39 Clues, which are ingredients to a serum that can create the most powerful person on Earth. This series' primary audience is age 9–14. Books 1-10 are paperback fair condition, book 11 is hardback very good condition. Willing to sell the books separately if needed, just message me which ones you are interested in.