Jack is an independent, resourceful eleven-year-old boy with a deep passion for elephants. Accustomed to his mother's unpredictable moods, he is fiercely protective of their bond and fears that involving authorities will result in his placement in foster care or with his estranged grandmother. He relies on his wits and his extensive knowledge of animal behavior to survive on his own in Maine.

Becky is Jack's mother, a tall woman with cropped blonde hair whose severe mental illness causes unpredictable mood swings. She oscillates between periods of absolute stillness and extreme, flighty energy, which she refers to as "spinning." Her instability forces Jack to act older than his age, though she also shares moments of whimsical connection and adventure with him.

Grandma is Becky's mother and Jack's maternal grandmother. Due to Becky's warnings, Jack views her as an intrusive figure who wants to separate him from his mother. She took Jack in temporarily during a past incident involving Social Services.

Big Jack is a helpful adult who encounters the young Jack in a bar while the boy searches for information about his mother. He assists Jack by splinting his injured pinky finger and teaches him that the word "mudo" means "thank you" in the Ewe language.

Sylvie is an eighth-grade girl who spots Jack wandering the streets and follows him to an internet café and bookstore. She recognizes him as the missing boy from the news broadcasts and becomes entangled in his efforts to stay hidden.

Wyatt is Sylvie's cousin who drives a van and encounters Jack on the road at night. He asks Jack a series of questions about his survival and his grandmother's financial situation.

Nina is Jack's best friend from his hometown in Massachusetts. She knows about Becky's unpredictable moods from past conversations, making her suspicious when Jack misses the beginning of the school year.

Aiden is a young boy vacationing with his family at Acadia National Park. He provides Jack with a brief, joyful distraction and represents the stable, conventional family dynamic that Jack secretly envies.

Julie is Aiden's sister. She vacations with her parents at Acadia National Park, forming part of the picturesque family unit that makes Jack feel both included and socially isolated.

Mrs. Olson is a woman who owns a small farm outside Bar Harbor. Instead of acting with anger when she catches Jack taking vegetables from her garden, she offers him a practical trade to help the local food pantry.

Lydia is a live elephant kept at an animal park in York, Maine. She represents Jack's ultimate destination and a point of contention between Jack and his mother, who opposes keeping animals in captivity.

Mudo is a small plastic elephant toy that Jack takes from a store. The toy serves as a constant companion for the isolated boy, offering him a tangible sense of security and courage during his lonely journey.