Jenny Jump is an important character in the four Oz books of John R. Neill.
Jenny begins as a fifteen-year-old in New Jersey, who one day finds a leprechaun stealing her cheese. She is clever enough to capture him with her stare, so that the leprechaun, called Siko Pompus, must grant her a wish. She wishes to become a fairy, and the leprechaun transforms her:
"The strangest things began to happen. Her toes on one foot began to tingle and want to dance. First one finger felt that it was tinkling like a silver bell, then another finger, and then another. Both of her ears were full of wonderful music, and she could hear the chairs talking to each other. One eye changed and saw everything with new and more beautiful colors. Even the old kitchen wall became as bring as a rainbow. She felt like the song of an oriole, and the murmuring of leaves. She felt as if everything were beautiful and happy."
In the midst of this psychedelia, however, Jenny's gaze falters, and the leprechaun eludes her control. She protests,
"Make me into a full fairy. I'm half girl and half fairy now. Only one eye is a fairy eye, and one foot; eight of my fingers are fairy fingers, and both of my ears. But I want to be all fairy."
But Siko Pompus refuses, for "'Twill only get ye into trouble."
Still, Jenny has remarkable new abilities. With her fairy foot, she leaps all the way to the Land of Oz, to begin her adventures.
Jenny is not a fan of the traditional, single-color fashions favored by the Ozites, and she sets up a shop with a magic turnstyle that dresses people according to their personalities.
Neill's text of The Wonder City of Oz was rewritten by an anonymous editor at Reilly & Lee, and that editor added some controversial changes to the story, in particular, involving Jenny Jump. These additions include creatures who live in the Deadly Desert called Heelers, who live on votes. Jenny is goaded into running against Princess Ozma as ruler of Oz. It is not taken very seriously by the Ozites, and it is decided that shoes will be used for votes in an Ozelection. The Ozelection and all that leads up to it is not in the manuscript. Furthermore, near the end of the novel, the Wizard casts a spell to make her younger and more obedient, some would say lobotomized. Neill was not enamored of these changes and did not illustrate them, and Jenny seems to have gone back to her old self in the two sequels.
Jenny is regularly accompanied by a Munchkin boy called Number Nine. She has him wear whistling breeches that alert her to his presence.
In The Runaway in Oz, Jenny helps get the story started by quarreling with Scraps the Patchwork Girl; but once Scraps runs away, Jenny spends the rest of the book helping to look for her.