Alex's best friend is not only nick-named Slug, he is a slug-a huge, orange Casper-the-ghost-like, cheerful slug. While no explanation is given for why Slug lives in a neighborhood of human beings, the fellow's irrepressible spirit adds humor to an otherwise familiar story of friendship. ""It used to be Slug, Kevin, and me-the unstoppable three,"" says narrator Alex, but when Kevin moves away, Slug's clingy friendship begins to annoy Alex, who needs ""some alone time."" Slug's friendly face and slithery body nicely mirror his feelings throughout, and Krosoczka's illustrations skillfully highlight Slug's irritating but likable character. Slug is constantly talking (""And in math class, the teacher was all, 'Slug, turn around and be quiet' and I was all like, 'Sorry, Mrs. Hass' ""). He blurts out the plot of a movie before they watch it, and even invites himself over to Alex's house-but he obviously means well. Krosoczka frequently adds more humor to the main text by including dialogue within the illustrations. While the two friends shop for clothes at the mall, for instance, the flame-toned Slug suggests, ""They're saying orange is the new black."" But when Slug overhears Alex tell his mother, ""I'm sick of him!"" the friendship seems in jeopardy-until Alex says he's ""really, really, really sorry!"" Despite the thinly veiled didacticism of the story (""Saying sorry is never easy""), this book about an unusual bond offers young readers insight into how a friendship can be restored with an honest apology. Ages 5-8.