Judy is a third-grade student who experiences intense emotional states she calls her "famous moods." She possesses a deep love for science and biology, especially examining mealworms in the classroom. After witnessing a classmate's academic recognition in the local newspaper, she becomes determined to achieve fame for herself through various creative schemes.

Stink is Judy's younger brother who enjoys a more relaxed approach to life. He inadvertently aggravates his sister by effortlessly achieving the recognition she desperately seeks, including a past newspaper mention for his unique birth. Despite his tendency to irritate his older sibling, he clearly admires her and eagerly participates in her projects.

Jessica is a third-grade student who achieves academic success through hard work and practice. She proudly displays her spelling bee victory and newspaper appearance, which sets off a wave of envy in her classroom. She maintains a friendly demeanor and actively attempts to invite others to spend time with her.

Frank is an easygoing third-grade student who sits beside Judy at school. He possesses a relaxed attitude that contrasts sharply with his friend's intense energy. He willingly goes along with group activities and consistently offers help, such as correcting spelling mistakes during class lessons.

Rocky is one of Judy's closest friends who frequently accompanies her on her adventures. He has a minor claim to fame from appearing in a library photograph. He readily joins neighborhood clubs and group experiments without demanding attention for himself.

Judy and Stink's mother and father maintain a calm and supportive household. They allow their children the freedom to learn from their own mistakes and natural consequences. Rather than lecturing, they observe their daughter's intense emotional shifts with passive patience.

Mr. Todd teaches third grade and manages a classroom of energetic students. He balances practical consequences for misbehavior with an understanding approach to childhood excitement. He creates engaging science lessons that capture his students' academic interests.

Laura is a young girl recovering from a recent heart transplant at the local hospital. She spends her recovery time in the playroom but finds the available toys dirty and unappealing. Her quiet resilience leaves a strong impression on the visitors she meets.

Mouse is the family cat who lives with the Moodys. He possesses the ability to push the button on a toaster to make toast, a trick his owner hopes will win a local pet competition. He tends to squirm when having his picture taken.