Crow is a twelve-year-old girl who washed ashore on a tiny Elizabeth Island just hours after her birth, crying hoarsely in a small skiff. Raised by the solitary man who found her, she feels deeply connected to the rugged island environment and spends her time beachcombing for interesting rubbish. Because the residents of the nearby island of Cuttyhunk fear she came from a former leper colony, they refuse to touch her or allow her into their school. This isolation fuels her intense curiosity about her origins and sets her on a determined search for the family that sent her away.

Osh is a solitary man from an unnamed foreign country who arrived in the Elizabeth Islands after intentionally wrecking his own boat. Refusing to speak for years, he finally found his voice when he took in the newborn Crow. He makes a meager living by catching lobsters and painting seascapes using homemade pigments and brushes made from cat fur. Deeply private about his own traumatic past, he worries that Crow's search for her origins will lead her away from the life they built together.

Miss Maggie is a fiercely independent woman who left a farming life far from the ocean to live in a smart little house on Cuttyhunk. She raises sheep, cows, and chickens, providing a vital lifeline of food and supplies to Osh and Crow. Unbothered by the superstitious fears of the other islanders, she takes it upon herself to educate Crow when the local headmaster turns her away. She acts as a blunt but caring anchor for her two isolated friends.

Kendall is a large, imposing man with a southern accent who poses as the gamekeeper of the new Penikese bird sanctuary. He acts openly hostile toward visitors, demanding they leave the island quickly. His sudden appearance, coupled with his aggressive questioning and physical intimidation, suggests he is searching the island for reasons completely unrelated to the birds.

Sloan is a thin, solitary man from Maine hired to work as the legitimate gamekeeper for the new bird sanctuary on Penikese. Because the island is uninhabited and avoided by locals, his isolated post makes him highly vulnerable to attack.

Miss Evelyn Morgan is a former nurse who cared for patients at the Penikese leper colony before relocating to Louisiana. Having witnessed the tragic realities of the colony, she possesses crucial knowledge about the island's former residents. However, past deceptions make her highly guarded about sharing her secrets with strangers.

Susanna is a former resident of the Penikese leper colony who faced the extreme hardships of forced quarantine. Her desperate decisions regarding her children shape the central mysteries of the island.

Elvan is a former resident of the leper colony on Penikese Island. He endured the harsh realities of medical isolation alongside his wife while trying to ensure a future for his family outside the quarantine zone.

Jason is the son of Susanna and Elvan who was sent to an orphanage in nearby New Bedford to protect him from his parents' illness. Growing up isolated and shunned by other children due to his origins, he eventually finds work as a sailor on the open sea.

Dr. Eastman is the former director of the Penikese leprosarium who currently resides in Louisiana. He maintains the official records and historical memory of the colony's residents, providing key facts to those trying to reconstruct the past.

Mrs. Pelham is a compassionate woman who worked at the New Bedford orphanage when Jason arrived from Penikese. She recalls specific details about the children under her care and offers a sympathetic perspective on the prejudice the orphans faced.

Quincy is a young sailor working aboard the schooner Shearwater. His labor puts him directly in the path of the dangerous storms that frequently cause wrecks around the craggy Elizabeth Islands.

Mouse is a pet cat who lives a quiet life in the makeshift cabin built by Osh. The cat provides constant, silent companionship to the small family.

Mr. Henderson is the headmaster of the local school on Cuttyhunk. Harboring deep-seated superstitious fears about contagion, he goes to extreme lengths to protect his students from perceived threats.

Mr. Benson is a townsperson living on Cuttyhunk. He serves as a source of local information, inadvertently passing along details that help others track the movements of strangers in the area.

Officer Kelly is a local policeman tasked with maintaining order in the remote Elizabeth Islands. He relies heavily on the observations of full-time residents to track down suspects who exploit the area's isolation.

Officer Reardon is a law enforcement official operating around Cuttyhunk and New Bedford. He assists in questioning locals and gathering evidence to track down dangerous fugitives.