Natalie is a seventh-grade student who uses her science notebook as a journal to record observations about her life. She struggles to understand her mother's recent behavioral changes and withdraws from her family members in response. Applying the scientific method she learns at school, she observes her surroundings and forms hypotheses about her home environment. She decides to enter a local egg-drop competition to win cash for a trip.

Alice is a botanist who previously researched rare cobalt blue orchids in a university lab alongside Dana Menzer. She currently spends her days in her bedroom, leaving her home greenhouse and its plants untended. Her extended absence from family activities prompts Natalie to view her as an unfamiliar version of her former self.

John is a professional therapist taking on extra household responsibilities like cooking meals. He attempts to manage the household while using cautious language to explain his wife's condition to his daughter. His reliance on his professional training during personal conversations occasionally frustrates Natalie. He grew up in a Korean household but does not actively practice those traditions in his adult life.

Twig is Natalie's wealthy and fiercely loyal best friend. Her parents are separated, and her father lives in New York, a topic she actively avoids discussing. She enjoys playing board games, bringing back glass figurines from her trips to Paris, and trying to engage the increasingly distant Natalie in school projects.

Mr. Neely is an energetic, optimistic science teacher who recently switched careers. He actively encourages his students to ask questions and suggests the egg-drop competition as a project for Natalie. His unabashed enthusiasm often draws gentle mockery from his students.

Dari is a highly intelligent seventh-grade student who participates enthusiastically in science class. He wears a Mr. Potato Head costume for Halloween and remains unbothered by others' opinions of him. He seeks to join the egg-drop competition and work alongside his classmates despite having the skills to compete alone.

Mikayla is a seventh-grade student who refuses to dissect frogs due to her beliefs about animal rights. She and Natalie were inseparable until the fourth grade, when their mothers worked together in a botany lab. Now, the two girls actively avoid each other in the school hallways.

Dana is a botanist who manages the university lab where Alice works. She previously studied rare cobalt blue orchids alongside Alice. Her professional decisions regarding the lab's budget and research findings make her a subject of Natalie's scientific hypotheses.

Dr. Doris is a professional therapist who meets with Natalie to discuss her family life. She maintains a gentle, patient approach during sessions while Natalie initially refuses to answer personal questions or engage with the process.

John's mother splits her time between Korea and California. She proudly embraces her Korean heritage and enjoys sharing traditional food with her family. Her holiday visits prompt Alice to make rare appearances outside her bedroom.

Janie is a middle school student in Mr. Neely's science class who shares Mikayla's views on animal rights.

Uncle Gene is Grandma's romantic partner who lives in California and spends time with her when she is not in Korea.