In Green Bank, West Virginia, two teens--grieving, artistic Copernicus and Kepler, a small-town overachiever--become secret pen pals through a forgotten astronomy textbook and join forces to unravel a decades-old mystery tied to Copernicus's late mother.

When a recent transfer student starts keeping her diary in the oldest textbook at the Green Bank High School library, the last thing she expects is to receive a response. Thus begins a sweeping tale of unlikely friendship and long-buried secrets between two secret pen pals at a rural West Virginia high school. Copernicus is adrift and searching for answers after the sudden death of her mother, and leaving her cosmopolitan life in San Francisco behind. Kepler is a small-town girl with straight A's and big plans to be the first person in her family to go to college, despite her family's modest means. The two girls are so different from one another but united in their goal to solve a mystery that has riddled Green Bank for decades.