Polly and Ruthie are sisters. At a young, young age Polly's talent for making pie is evident- as the author notes, "even her mud pies were a cut above the others in the sandbox." Ruthie could sing like an angel. But. For whatever reason Ruthie decided to focus her energy on being jealous of Polly instead of developing her singing. She is a bitter wife, a bitter mother, and a bitter, jealous sister. Really too bad. Especially bad for Alice her daughter and her husband who bear the brunt of her malevolence. This is because Polly is focused entirely on having a great time and doesn't pay attention to Ruthie's grumpiness.
Alice spends each Saturday with Aunt Polly at PIE, Polly's shop. When Ruthie and Polly's parents died the inheritance was split. It is unclear what happened to Ruthie's half, Polly realized she could live on the money and open a PIE shop. She surprised the entire town by refusing to take any money for the magical, wonderful, exceptional pies in her shop. The result was a brisk barter system. Peaches, tomatoes, grapes, pecans, flour.... would appear in her doorway overnight and she had no end of ingredients for her pies.
One day, she feels unwell and overnight she dies kicking off a huge controversy about where her famous crust recipe might be. This is a mystery that must be solved by the ever imaginative Alice. In the course of solving this many old conflicts find resolution.