WANTED:One young woman to take care of a four-year-old boy.Must be bordering on masochistic.Must relish sixteen-hour shifts with a nap-deprived pre-schooler.Must love getting thrown up on, literally and figuratively, by everyone in his familyMostly, must love being treated like fungus found growing out of employers Hermès bag.Those who take it personally need not apply.Who wouldn't want this job?Nanny is a struggling grad student with no visible piercings. Mrs. X, of Park Avenue, doesn't work, clean, cook, or raise her own child. She makes appointments and lists. Nanny needs a job. Mrs. X needs someone accommodating. Nanny and Mrs. X need each other. In return, Nanny is subjected to erratic shifts, irregular paychecks, and the sullen moods of her four-year-old charge. Sentenced to every play date known to Central Park, and every gourmet-snack run she can handle, Nanny needs a diversion that an afternoon martini can't fulfill. Then she discovers a secret about Mr. X. Navigating a marriage on the rocks and the increasingly paranoid, impossibly demanding attitude of her employer, Nanny is redefining servitude. Because now, Nanny has something worth more than Mrs. X's ill-fitting Prada castoffs as a thankless bonus. Nanny's acquiring the power of revenge…