Calpurnia Virginia Tate is eleven years old in 1899 when she wonders why the yellow grasshoppers in her Texas backyard are so much bigger than the green ones. With a little help from her notoriously cantankerous grandfather, an avid naturalist, she figures out that the green grasshoppers are easier to see against the yellow grass, so they are eaten before they can get any larger.

As Callie explores the natural world around her, she develops a close relationship with her grandfather, navigates the dangers of living with six brothers, and comes up against just what it means to be a girl at the turn of the century.