Mary Lou is a thirteen-year-old girl caught between the carefree days of childhood and the confusing onset of adolescence. Living in Easton, Ohio, with her large, noisy family, she feels left behind by her boy-crazy peers and uses reading to process her world. She is observant, sometimes defensive, and prone to analyzing her life through the lens of ancient Greek mythology.

Carl Ray is Mary Lou's seventeen-year-old cousin from rural West Virginia. Tall, pale, and intensely quiet, he visits Easton under the guise of looking for a job. His silent presence frustrates Mary Lou, but he gradually reveals a sensitive nature and a deep knowledge of classical texts that surprises his relatives.

Alex is a thirteen-year-old classmate of Mary Lou who lives in a wealthy, quirkily decorated house on the other side of town. Graceful and athletic, he frequently wanders around Mary Lou's neighborhood over the summer. Despite speaking mostly in monosyllables, he shares Mary Lou's interest in reading and quietly pursues a connection with her.

Beth Ann is Mary Lou's thirteen-year-old best friend who lives in a highly organized household. Over the summer, she becomes intensely focused on dating, fashion, and joining exclusive social clubs. Her shifting priorities cause tension with Mary Lou, highlighting the differing paces at which the two girls are maturing.

Mr. Furtz is a tall, freckled neighbor roughly the same age as Mary Lou's father. He runs a local hardware store and holds a mysterious, quiet connection to Aunt Radene's past.

Sam is Mary Lou's father, a geologist who originally hails from a large West Virginia family. He attempts to maintain authority over his chaotic household while avoiding direct conflict whenever possible.

Sally is Mary Lou's mother, who works as an oral historian. As a busy working parent, she relies heavily on her children to manage household chores and goes out of her way to present a civilized image to guests.

Maggie is Mary Lou's seventeen-year-old older sister. Preoccupied with clothes, makeup, and her social life, she frequently charms her way out of trouble and dodges her responsibilities at home.

Dennis is Mary Lou's twelve-year-old brother. He is caught in the awkward stage between childhood and adolescence, still enjoying tree-climbing while beginning to mock his sister's interest in boys.

Dougie is Mary Lou's eight-year-old brother. Skinny and serious, he is quieter than the rest of his boisterous siblings but possesses an excellent memory.

Tommy is the four-year-old youngest child of the Finney family. Adored by his parents and siblings, he easily charms everyone he meets.

Uncle Carl Joe is Sam's brother, living on a primitive farm in West Virginia. He chews tobacco, rarely travels, and holds firm, traditional views on family loyalty.

Aunt Radene is Uncle Carl Joe's wife and the mother of seven children. Originally from Easton, she adapted to life in rural West Virginia and acts as the family's primary correspondent, though she frequently appears anxious and overwhelmed.

Mrs. Furtz is the neat, highly organized wife of the local hardware store owner. She initially looks down on the boisterous Finney family but becomes heavily involved in their lives following sudden neighborhood events.

Christy is a popular, boy-crazy classmate who founds an exclusive social club. She actively seeks attention and views middle school primarily as a hierarchy to climb.

Mr. Birkway is the new English teacher at Mary Lou's school. Though he does not directly appear in the summer events, he serves as the unseen audience for Mary Lou's diary.