The Empty Envelope (A to Z Mysteries Series #5)

E is for Envelope...Dink keeps getting envelopes in the mail addressed to "D. Duncan." But the letters inside all start with "Dear Doris" and don't make any sense! Josh and Ruth Rose think someone's playing a trick on Dink. But Dink is sure there's more to it than that, especially after Doris herself shows up and demands her letters!