If you come to Seabird Island you will want to visit the Treasure Chest Seashell Shop. There is a large, old trunk in the shop window. Sage and Sam spend their family vacation helping Aunt Lacey and Uncle Jonah in the shop. Annie their dog, and Albert their cat are there too. One night, Sage and Sam make a choice. It leads them to an unexpected discovery in the seashell shop. Will they solve the mystery before they leave Seabird Island? Is there a message in the treasure chest?