Harriet M. Welsch is determined to grow up and be a famous author. In the meantime, she practices by following a regular spy route each day and writing down everything she sees in her secret notebook.

Then one morning, Harriet's life is turned upside down. Her classmates find her spy notebook and read it out loud! Harriet's in big trouble. The other sixth-graders are stealing her tomato sandwiches, forming a spy-catcher club, and writing notes of their own -- all about Harriet!