Eight-year-old Mackenzie Goode has a sense of humor that always gets her into trouble. But in third grade, she makes the ultimate promise to herself: no more mistakes. Mistakes are for babies and the last huge mistake she made, back in second grade, caused her a forever grounding and to see a look in her parents' eyes she never wants to see again: disappointment. When the principal of the school visits Mac's class as a mystery reader, Mackenzie's...