Signed by author Penny Warner! Cody, Quinn, Luke, and M.E. may not have much in common with each other, but they do 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 their neighbor's house?the neighbor 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. Meet super sleuths Cody, Quinn, Luke and M.E., members of The Code Busters Club. Together they decipher mind-boggling problems and crack the toughest of codes! These fast-paced stories are perfect for young detectives eager to solve fascinating mysteries. Every title contains 15 extra riddles for readers to solve, with a handy Key Code index to help those who get stuck! This four-book Agatha Award-winning series is perfect for middle-grade readers looking for an adventure!