The Secret of the Skeleton Key (The Code Busters Club #1) by Penny Warner

Cody, Quinn, Luke, and M.E. may be really different, but they all share one thing in common: they love playing around with codes. In fact, they love codes so much, they have their own private club, with a super-secret hideout and passwords that change every single day.

When Cody and Quinn notice what could be a code on the window of a nearby house, the one owned by their strange neighbor, the guy they call Skeleton Man, the club gets to work. And it is a cry for help!

Now the Code Busters are on the case—and nothing will stop them from solving the mystery and finding the secret treasure that seems to be the cause of it all!

This exciting interactive mystery offers more than fifteen codes for you to decipher, including the Consonant code, Morse code, and American Sign Language. Test your brain with the Code Busters and solve the mystery along with them. Answers are in the back, if you ever get stuck.