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 is an only child who has mostly been raised by her nanny, Golly, 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 and overburdened Sport. Harriet's world begins to change when Golly leaves, signaling that it is time for her to grow up. Then a snobby girl from 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.