Ernest is a 12-year-old boy in the seventh grade living in a San Francisco apartment. He prefers reading dictionaries and memorizing definitions over reading fiction or socializing with peers. Following an unspecified family struggle, he has withdrawn into silence, choosing to escape to the roof rather than talk to his parents or siblings. When his mother disappears, his quiet guilt drives him to investigate her whereabouts alone.

Olivetti is a sentient, older-model Lettera 22 typewriter belonging to the Brindle family. He possesses thoughts, feelings, and a perfect memory of every word ever typed on his keys. He holds strong opinions about the superiority of typewriters over computers and secretly watches the family grow. When his usual routine shatters, he contemplates breaking the sacred rule of his kind by communicating directly with a human.

Quinn is the confident daughter of the local pawnbroker. She frequently searches dumpsters to collect discarded items, finding value in things others throw away. After recognizing a missing person from her father's shop, she inserts herself into the search efforts. She asks direct questions and refuses to let others push her away.

Beatrice is a mother of four and an avid writer who previously relied on a vintage typewriter to catalogue her personal memories. After receiving a distressing phone call, she abruptly pawns her typewriter, discards her manuscripts, and vanishes without warning. Her sudden emotional departure leaves her family panicked and confused.

Felix is a businessman and father of four who relies heavily on routine to manage stress. He attempts to keep his children on schedule with school and extracurriculars despite the crisis of his wife's disappearance. His insistence on maintaining a sense of normalcy frequently causes friction with his children.

Ezra is a high school student and the oldest of the Brindle brothers. He dedicates his time to fitness and weightlifting, displaying a tough exterior to the rest of the household. He reacts to family stress with anger and rigid routines, frequently using a rough, teasing approach when dealing with his younger siblings.

Adalynn is a high school student involved in theater. She types sharply and rapidly, moving through life with a quick, commanding presence. She often covers her own anxiety by adopting a bossy attitude, directly ordering her younger brothers to change their habits or adhere to the family schedule.

Arlo is the youngest of the Brindle children. He attends elementary school, wears oversized hand-me-downs, and enjoys rescuing frogs from the apartment roof. He types with a messy, uncoordinated style and views the family's stress with a more innocent, naive perspective than his older siblings.

Mr. Corrie, whom his daughter calls "Pop," owns and operates the Heartland Pawn Shop. He completes a transaction for a vintage typewriter from a visibly distressed customer, paying her $126. Though he feels awkward about her crying, he maintains a pragmatic approach to his business.

Remi is a Remington-brand typewriter sitting on a shelf in the Heartland Pawn Shop. She previously lived in a bookstore where patrons typed wishes on her keys. She communicates with other typewriters by striking her keys against an empty carriage roll, offering a cynical perspective on human nature.

Mrs. Vivian runs the local public library, which faces permanent closure due to a lack of patrons. She knows the Brindles from their frequent past visits for story hour and tracks the borrowing habits of the few remaining people who walk through her doors.

Thiago is the maintenance man at the apartment building where the Brindles live. Having immigrated from Brazil, he deeply appreciates the kindness he receives from certain tenants and closely observes the daily routines of the building's residents.

Dr. Branson is a local physician whose office sits along the number 12 bus route. He works with patients dealing with serious medical conditions and maintains a strict, clinical schedule. Ernest initially seeks him out believing he is a therapist.