Sempronious is 12 but not quite 12 ½. He lives in Asheville, NC, where he becomes obsessed with an address: 12 ½ Wall Street. He is a flirt, takes in a bit too much sugar, and speaks his mind. Sempronious' nickname is "Sly." Sly enjoys being sly, and is curious about his world, especially 12 ½ Wall St. Soon, his curiosity gets the better of him regarding two things: the mysterious address and a giant iron at the corner of Wall St.
Sly makes an appointment with the mayor in order to learn more about 12 ½ Wall St. and the iron. Soon thereafter, Sly finds himself on Asheville's Urban Trail, a "museum without walls," with the girl of his dreams. He meets an assortment of characters who want him to fulfill his destiny, which is to write a book about his experience. Through it all, Sly learns more about life than he was expecting.