A tantalizing question, that--though Jasner (pseudonym, the book notes, for Jane Werner Watson) doesn't get to the switch between Jenny, in Halloween witch garb, and real little witch Peckity Hecate until page 14, and then doesn't give it much snap. Practical brother Nick has been scoffing at Jenny's liking for ""witchy things,"" so it's understandable that she succumbs to Peckity Hecate's blandishments (""Let's have some fun. Let's trade places"") and relinquishes her treat sack and prop-broom for the little witch's ""real"" broomstick. But once transported to the mountaintop haunt of the old-hag witches, she shudders at their demands for toads and bats' wings; and then is exposed--""What are you--a real little girl?""--when the resident black cat raises its back and hisses. Peckity Hecate, meanwhile, is doing some shuddering too--every time Dad (""Come on in, dumpling"") pats her on the back; and the jig is up for her when it's suggested she take off her mask. An original situation, illustrated with passable Charles-Addams puckishness--which helps offset the somewhat uninventive development.