Mia is a 10-year-old Chinese immigrant who helps her parents manage the Calivista Motel in Anaheim, California. Despite her youth, she resourcefully takes over the front desk duties to give her parents time to clean rooms, staring down adult guests who question her authority. She has a strong passion for the English language and dreams of becoming a writer, hiding a tip jar to save up the $300 entry fee for an essay contest.

Mia's parents, Mr. and Mrs. Tang, are hardworking professionals from China who take menial jobs in America to survive. Mr. Tang, a former engineer, is a gentle dreamer who collects flawed pennies and encourages his daughter's writing. Mrs. Tang is highly practical and pushes Mia to focus strictly on math, fearing she will never write like a native English speaker. They endure poverty and frequent mistreatment because they believe they have no other options for survival.

Mr. Yao is the wealthy, miserly owner of the Calivista Motel. He systematically takes financial advantage of his employees and tenants, docking the Tangs' pay for guest refunds, arbitrary expenses, and broken equipment. He holds overt prejudices against Black guests and insists that good employees must "know their place."

Hank is a middle-aged African American man who rents a room at the Calivista Motel on a weekly basis. He forms a close bond with Mia and her parents, becoming a core part of their chosen American family. He faces pervasive racial discrimination in his daily life and from local police, initially taking a resigned, passive view of the injustices he experiences.

Jason is Mr. Yao's 10-year-old son and the only other Chinese student in Mia's fifth-grade class. He experiences intense pressure from his father to learn the motel business and adopt his ruthless management style. His interactions with Mia are characterized by rudeness, mockery of her clothing, and petty theft, masking his insecurities and complicated feelings about her.

Lupe is a 10-year-old Mexican immigrant who becomes Mia's closest friend at her new elementary school. She initially attempts to hide her family's poverty by pretending to be wealthy, but she and Mia soon bond over their shared financial struggles when Mia discovers Lupe's father is the motel's cable repairman. She provides Mia with emotional support and shares an analogy about the distinct "roller coasters" for rich and poor people.

Mrs. Douglas is Mia and Jason's fifth-grade teacher. She facilitates classroom activities and assigns writing tasks, attempting to manage the interpersonal dynamics among her students while occasionally missing the deeper cultural and economic realities her immigrant students face.

Uncle Ming is not a biological relative but a former coworker of Mr. Tang from a Chinese restaurant. He stays with the family while waiting for his car radiator to be repaired, representing the severe physical and financial dangers vulnerable immigrants face.

Billy Bob is one of the "weeklies"—the long-term residents of the Calivista Motel. He is part of the tight-knit community that welcomes Mia and helps form her extended American family. He proudly displays a security sticker on his car despite not actually having an alarm system.

Fred is another weekly resident at the Calivista Motel. He participates actively in the communal life of the motel's long-term guests, offering immediate friendship to the newly arrived Tang family.

Mrs. Q is a weekly resident at the Calivista Motel who provides emotional support to Mia. She comforts Mia on the stairwell when the young girl feels overwhelmed by her mother's harsh criticisms about her English skills.

Mrs. T is a long-term resident of the Calivista Motel who actively supports Mia's ambitions. She lends Mia a dictionary and a thesaurus, providing crucial tools for the young girl to draft letters and improve her English vocabulary.

Uncle Li is an immigrant friend of Uncle Ming who seeks temporary refuge at the Calivista. He shares stories of extreme workplace exploitation, including an employer who fed workers nothing but mayonnaise on white bread, inspiring Mia to start a journal of abusive employers.

Aunt Ling is an immigrant worker who stays at the motel to escape abusive employment conditions where she is forced to kneel all day. Grateful for the Tangs' hospitality, she repairs Mrs. Tang's cleaning-damaged nails and suggests creating a secret signal to warn immigrants when Mr. Yao is present.

Uncle Zhu is an immigrant traveler heading to San Diego who stays with the Tang family. Mia enlists his help to investigate the addresses of specific suspects related to a stolen car at the motel because the police refuse to look into them.

Uncle Fung is a befuddled immigrant guest at the Calivista Motel who struggles with American cultural norms and etiquette, accidentally offending customers. Mia writes a helpful pamphlet for him to prevent future workplace misunderstandings.

Xiao Zhang is a highly skilled former engineer who has been reduced to working in a restaurant where the owner confiscated his passport. He escapes a workplace immigration raid through a secret tunnel system and stays at the motel while trying to figure out how to recover his documentation from his abusive employer.

Cousin Shen is Mia's relative back in Beijing. His letters highlight the contrast between his family's growing wealth and upward mobility—including a spacious new apartment and a car—and the Tang family's extreme poverty and struggles in America.