It's the summer of 1987 in the dying New England mill town of Swift River, and sixteen year-old Diamond Newberry is learning how to drive. Since her father disappeared seven years ago, she and her mother hitchhike everywhere they go; they're the only people in town without a car. But that's not the only reason Diamond stands out: She weighs 298 pounds, and since Pop's been gone, she is the only person of colour in all of Swift River.

This summer, Ma is determined to declare Pop legally dead so that they can collect his life insurance money, get their house back from the bank and move on with their lives. When Diamond receives a letter from a relative she's never met, key elements of her father's past are uncovered, and she is introduced to two generations of African American Newberry women, spanning the twentieth century and revealing a much larger picture of prejudice and love, of devotion and abandonment. As more letters come, they fill in the pieces of her history she never knew she was missing, giving her a sense of her place in the world and her family.

But what will she do with what she's learned, and will it mean having to leave Ma?