Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and they're getting strange notes from a mystery messenger!   It's time for the annual Greenfield art contest, and the Alden children are right in the middle of things, meeting the artists and learning about art! But when they receive a mysterious message signed the "Tattletale," they realize hat not everything about the art world is as it seems. What could the Tattletale want from the Aldens—and who is this mysterious message-writer? It's a painting puzzler for the Boxcar Children!