Imagine checking your mail and finding a letter that is completely empty. That is exactly what happens to Dink, and it is only the beginning of a very strange week! Envelopes keep arriving addressed to someone named D. Duncan, but the letters inside are written for a person named Doris. To make things even more confusing, one of the envelopes has absolutely nothing inside it. Dink, Josh, and Ruth Rose are convinced that this empty envelope is actually a secret code waiting to be cracked. Put on your detective hat and help the trio figure out who is sending these confusing letters. You will need to use your best problem solving skills to uncover the hidden message and solve this alphabet mystery.