Henry, Jessie, Violet, and Benny used to live alone in a boxcar. Now they have a home with their grandfather, and are going to help out at the Pretty Bird Pet Shop.   The Aldens are thrilled to have the chance to work with the animals at the pet shop. But things just aren't going smoothly. The Aldens' deliveries of pet supplies keep getting mixed up. And someone has let the birds out of their cages. It's up to the Boxcar Children to find out who's behind all the trouble!