The first feature film from the Nickelodeon cable channel, Harriet the Spy is an updated version of Louise Fitzhugh's best-selling 1964 children's novel. Sixth grade outcast Harriet (Michelle Trachtenberg) is an only child who has mostly been raised by her nanny, Golly (Rosie O'Donnell), rather than her materialistic parents. Harriet wants to be a writer when she grows up, and only Golly encourages her creative pursuits. Meanwhile, Harriet dons a yellow raincoat and a belt full of gadgets to spy on everyone around her, including her eccentric neighbor with a lot of cats and the other kids at school. Carefully taking notes in her private notebook, Harriet makes clever and cruel observations about her subjects, including her best friends, would-be scientist Janie (Vanessa Lee Chester) and overburdened Sport (Gregory Smith). Harriet's world begins to change when Golly leaves, signaling that it is time for her to grow up. Then a snobby girl a school, Marion, gets her hands on Harriet's special notebook and makes its contents known to the whole school. Soon everyone is against Harriet, and she must concoct a plan to get even.
~ Andrea LeVasseur, All Movie Guide