Mary is an 11-year-old girl living on Martha's Vineyard in 1805. Born deaf, she lives in a community where a large portion of the population shares her condition and everyone communicates using a local sign language. She possesses a highly imaginative mind and dreams of becoming a teacher. However, she carries a hidden burden of guilt over the recent accidental death of her older brother.

Mrs. Lambert is Mary's hearing mother, who seamlessly uses sign language to communicate with her deaf husband and daughter. She suffers from deep grief following the tragic death of her teenage son, George, which causes her to withdraw from church activities. Though loving toward her immediate family, she holds rigid views about social class and racial hierarchies.

Mr. Lambert is Mary's deaf father and a prosperous landowner on Martha's Vineyard. He serves as a steady moral anchor for his household. Unlike many of his neighbors, he possesses egalitarian views, stubbornly hiring marginalized workers despite the community's prevailing prejudices.

Andrew is a young scientist and student from Yale University who visits the island to study its high population of deaf inhabitants. He holds heavily prejudiced views, believing deafness is a disease and assuming those who are deaf possess lower intelligence. His invasive research methods and condescending demeanor quickly cause friction with the local community.

Ezra is a deaf, retired seaman who lives in a humble cottage near the Lambert home. He is an animated storyteller who uses full-body expressions to share tales of his past as a Revolutionary War privateer. He provides Mary with encouragement and a tangible link to the island's history.

Nancy is Mary's hearing best friend, highly proficient in the island's sign language. She is an artistic girl with a specific gift for playing the recorder. Nancy's loyalty to Mary is sometimes tested by her impatience and the biases she inherits from her temperamental parents.

Dr. Minot is a prosperous Boston physician and Andrew Noble's academic mentor. He holds a strong interest in studying deafness and sponsors Andrew's expedition to Martha's Vineyard. He belongs to the rigid, hearing-centric society of Boston, viewing the islanders' condition as an anomaly requiring scholarly investigation.

Thomas is a Black freedman originally from Maryland who works as a hired hand on the Lambert farm. Fluent in sign language, he fully integrates into the Wampanoag community through his marriage. He challenges the island's strict racial hierarchies by valuing cultural kinship over skin color.

George is Mary's late teenage brother, a hearing boy whose memory casts a long shadow over the Lambert household. He died eight months prior to the story's events while pushing Mary out of the path of a runaway carriage. He was a talented artist who drew a special map of the island that Mary deeply cherishes.

Reverend Lee is the local minister in Chilmark who preaches sermons about neighborly compassion. He facilitates Andrew Noble's visit to the island by hosting the young scientist, initially unaware of the severe friction his guest will cause among the residents.

John Skiffe is Nancy's father, a local landowner known for his bad temper. He engages in a bitter legal and social dispute, aggressively attempting to claim land that legally belongs to the Indigenous Wampanoag people.

Sally is the young daughter of Thomas Richards and his Indigenous Wampanoag wife. She is an observant girl with a strong connection to animals and a healthy distrust of the island's strange new visitor.

Miss Hammond is Mary's schoolteacher, who strongly encourages the young girl's reading and writing abilities. She is forward-thinking and supportive, recognizing Mary's natural talent for storytelling and her academic potential.

Mr. Pye is Miss Hammond's suitor. During a dinner party with the Lamberts, he demonstrates logical thinking by openly challenging Andrew Noble's flawed scientific theories about the environment causing deafness.