This is one of the books from my childhood that created a strong enough impression on me that I still remember it to this day. Codes and ciphers always had an aura of mystique about them--spies used them, and spies were cool, so when we used them, we were cool too! This book provided the foundation for a lot of the knowledge of (basic) cryptography I have now, and encouraged me as a homeschooler to delve deeper into the subject. Though the writing is not that of Koontz, King, Bradbury (or Shakespeare for that matter), the story is enjoyable and even entertaining. I would suggest this book as something for grade schoolers to read if they are interested in the subject matter.