After shy cello player Harriet Henry accidentally knocks the moon out of the sky, the moon becomes her friend, and Harriet gains the courage to share her music.
Twelve-year-old Agnes hates everything about herself, starting with her name, so while spending a summer with her father, a cellist, she decides to become someone else.
Told in two voices, cellist Jubilee and anxiety-ridden Ridley meet at a comic con where both of their families have booths, and begin a relationship they must hide from their parents.