Peter's know-it-all sister Arlene, who's ten, scoffs when he gets a magic set for his eighth birthday: he's not old enough. But Peter has sense enough to read the directions--which is one thing Arlene fails to do before accidentally turning herself into a frog. Peter's quest to find out how to change her back takes him to several advisors--who tell him in turn that ""old answers are the best,"" he should ""go to the library,"" and he should use something he knows already. Sure enough--an old story gives him the idea of kissing his frog-sister; herself again, Arlene treats Peter with more respect. This thoroughly satisfying comeuppance is told with deft humor and many a clever twist; Delaney's full-color illustrations add to the fun. An ""I Can Read"" book.