The 39 Clues Book 6 In Too Deep

The 39 Clues is a series of adventure books that are published by Scholastic. The main part of the series is ten books revolving around the adventures of siblings Amy and Dan Cahill. They agree to the offer in their grandmother Grace's will and search for 39 clues scattered around the world. Rick Riordan wrote the first book and the main story arc, but other authors will write the rest of the books in the series. Five have been released and written (in order) by Rick Riordan, Gordon Korman, Peter Lerangis, Jude Watson, and Patrick Carman.[1] The rest will be written (in order) by Jude Watson (again), Peter Lerangis (again), Gordon Korman (again), Linda Sue Park, and Margaret Peterson Haddix.[1]

The series also combines online gaming and card collecting along with the reading into a unique, interactive experience. Six cards come with every book, and more are sold separately in Card Packs. There are also activities related to the 39 Clues online.

There are also prizes for children between the age of six and fourteen. It is possible to win prizes by buying the books and playing the online game.

The books are also designed to teach history. The main characters are fictional, but in this series, almost every famous person belongs to the Cahill family. Because of this, Amy and Dan have to learn about these people to search for the Clues.