Harriet the Spy.

Harriet may only be in the sixth grade, but she's already found her calling: to be a spy. In a private journal she takes everywhere, Harriet records suspicious activity and keeps a running list of observations on virtually everyone she knows. It seems harmless enough until, one day, someone finds the journal and exposes Harriet's critical thoughts about her classmates. Suddenly, even her best friends are against her, and Harriet resolves to take revenge.