A competently contrived but unexceptional item about ""peanut-brain"" Mark (his sister's designation), who wants a dog and finally gets a guinea pig. Mark can't seem to do anything right, and that bothers him--until he meets a witch who can't do anything right either. Because he helps her, she offers to grant him a wish; but the spell goes wrong, and instead of a puppy she comes up with a stegosaurus. A second try produces a guinea pig, which Mark is willing to accept; and the witch now manages the harder job of making Mark's parents accept his pet. Thus Mark and the witch encourage each other, and Mark proves good at something--taking care of his pet. Along with the obvious bolstering functions there are some minor cute touches, based on Mark's and the witch's common klutzy tendencies. The pictures are second-class De Paola, with the people colored light brown. An acceptable filler.