A feeble concoction, far below the Lexau standard. On the first page, we hear that Willy Nilly's little sister Tilly has caught poison ivy; on the second page, he denies that he let her out of the yard. For the remaining 49 pages, the ""mystery"" is how Tilly caught poison ivy otherwise; and the answer--you can catch it from a pet--eventually comes out of a library book. But mostly Willy Nilly is occupied with one Miss Happ, who is certainly eccentric and may or may not be a witch. Like either, she stirs up a magic brew for Willy to pour on Tilly's head; like all parents, Willy's are exasperated. Lots of ""eyeball-to-eyeball"" talk between Willy and Miss H. does bring the solution closer--but not nearly quickly enough for a situation scaled to one short episode.