Ruthie has an imaginary friend who reflects Ruthie's feelings and takes the blame for whatever mischief is going on--in spite of Ruthie's parents' occasional exasperation: ""There is no Jessica."" Still, Jessica goes along for comfort on the first day of kindergarten. But when it's time to line up, a girl asks to be Ruthie's partner; amazingly, her name is Jessica, and she and Ruthie become instant pals. There's nothing unusual here, but diminutive, solitary Ruthie is engaging, vigorous, and self-possessed, like children in Sendak's early books. Pleasant treatment of a common theme.