Tess is an 11-year-old girl who lives on Bethsaida, a small island off the coast of Maine. Deeply attached to her home and fearful of having to move to the mainland if her school closes, she is determined to make her family's new foster placement work. She is highly superstitious, relying on a collection of lucky charms and rituals to manage her anxiety about the future. She loves the island's natural beauty and hopes to one day work on the water like her father.

Aaron is a 13-year-old boy whose bright red hair immediately marks him as an unlucky outsider among the superstitious fishermen. Placed in state care at age five and grieving the recent loss of his grandmother, he is defensive and reluctant to form new attachments. He is a highly talented musician who plays the piano and trumpet, using art to process his anger and maintain a link to his past.

Eben is a local boy and a long-time bully to Tess. Feeling ignored by his own parents, he acts out cruelly to gain attention and asserts dominance by targeting other children's vulnerabilities. He is quick to mock Aaron's red hair and foster status, jeopardizing the delicate process of making the new arrival feel welcome.

Mr. Brooks is a hardworking lobsterman whose livelihood is tied to the unpredictable waters around Bethsaida. He initially has ethical reservations about fostering a child simply to save the local school but fully commits to providing a safe, caring home. He is an emotionally available father who patiently works to earn the trust of his new foster son.

Mrs. Brooks is the only teacher at the small island schoolhouse. She is pragmatic and persuasive, convincing her husband that their strong family can help a child in need while simultaneously keeping the school open. She is a firm but nurturing maternal figure who values fairness and helps her children talk through their difficult emotions.

Ms. Spinney is Aaron's biological mother, whom he has not seen since he was five years old. She struggles with an alcohol addiction that originally led to Aaron's placement in the state system. Though she expresses love for her son through letters, her prolonged absence makes her relationship with him incredibly strained.

Libby is Tess's five-year-old sister. Eager and energetic, she looks forward to having a new older sibling as a playmate. She spends much of her time playing board games with friends and navigating the excitement of a growing household.

Natalie is the state caseworker responsible for Aaron's placement in the foster system. She is observant and protective, requiring families to adhere to strict visitation rules to ensure the safety of the children under her supervision.

Jenna is a classmate of Tess's who lives on Bethsaida. Her family is fostering a young girl, providing Tess with a peer who understands the unique challenges and shifting dynamics of bringing a new child into the home.

Grace is a young girl placed in foster care with the Ross family. She quickly integrates into the playgroup of younger children on the island, highlighting the broader community effort to save the local school.

Amy is Tess's former best friend who recently moved off the island. Her departure leaves a gap in Tess's social life, intensifying Tess's need to forge a successful connection with her new foster brother.

Reverend Beal is a local religious leader who proposed the community-wide plan to restore the island school's enrollment. He encourages local families to foster children and supports the youth by praising their talents.

Mrs. Coombs is an island resident in charge of entertainment for the annual Fourth of July picnic. She organizes musical performances and expects strict adherence to tradition from the participants.

Doris is a neighbor of the Brooks family who lives close enough to hear the activities in their home. Her appreciation for live music sparks an idea to help integrate the newest island resident into the community.

Mr. Moody works at the local post office. He represents the close-knit, sometimes intrusive nature of the small island community where everyone knows their neighbors' daily business.

Mr. Phipps runs the local gas and grocery store on Bethsaida. His shop serves as a central hub for the island's gossip, news, and daily provisions.