A mild mystery for middle graders: Fifth-grade Gabby decides to be a private eye for career day, so she looks into a series of puzzling neighborhood problems. For only 25 cents a day (plus expenses), Gabby sets about finding Miss Haliber's missing umbrella, Mrs. Driscoll's garden ornament, and other missing items. After following several false clues, she stumbles on the culprit responsible for their loss--a classmate intent on his own career-day project. A pesky little sister, a teasing fifth. grade boy, a missing pet caiman, and understanding parents round out this adventure in which adults are addressed as ""Ma'am"" and children are called ""My dear."" The heroine is neither as clever nor as contemporary as Gift's gift detectives; the jacket illustration is unappealing. Acceptable where gentle mysteries with girl protagonists are in demand.