Joanna is a graduate student studying bird ecology and nesting habits. She lives in an isolated forest cottage to complete summer research for her doctorate, working long hours to compensate for two years lost to breast cancer treatment. Still grieving the recent death of her mother from the same illness, she is self-conscious about her post-surgery body and prefers a quiet, solitary routine until a mysterious child disrupts her life.

Ursa is an enigmatic, highly intelligent young girl who appears out of the forest claiming to be an extraterrestrial from the Pinwheel Galaxy. She insists she is inhabiting a dead girl's body and refuses to reveal her earthly origins or true name. Her stated mission is to witness five miracles on Earth before returning to the stars. She readily reads college-level ornithology texts and classic literature to pass the time.

Gabriel is Joanna's neighbor who sustains himself by selling eggs at a roadside stand and raising animals on his family's farm. He lives with his ailing mother and struggles with social anxiety, depression, and agoraphobia, which caused him to drop out of college years earlier. He sports a heavy beard and initially acts defensive, but he quickly becomes an active participant in caring for Ursa during the daytime hours.

Tabby is Joanna's closest friend from their undergraduate years, currently enrolled in a veterinary program. She maintains a vibrant, free-spirited aesthetic, often wearing purple boots, a nose ring, and brightly colored streaks in her hair. She provides emotional support to Joanna regarding her cancer recovery and enthusiastically connects with Ursa over their shared love for the color purple.

Lacey is Gabriel's sister, older than him by nineteen years. She frequently visits the family farm to care for their mother and manage the property when Gabriel's mental health prevents him from working. She harbors long-standing resentment toward her brother, often belittling his intelligence and actively attempting to keep Joanna and Ursa away from him.

Katherine is Gabriel and Lacey's mother, who lives on the farm where she and her late husband built their home. She is a former poet who has published two volumes of work, though Parkinson's disease now prevents her from writing or typing. She relies on her children for care and expresses quiet concern over Gabriel's isolation.

Little Bear is a stray dog living in the woods near Joanna's rented property. He is initially wary of human contact until Ursa wins his trust with marshmallows and her gentle demeanor. Ursa names him after the Ursa Minor constellation, and he becomes her constant companion and protector around the cottage.

Dr. Shaw Daniels is Joanna's academic advisor for her graduate studies in ornithology. He monitors her summer research progress and shows professional concern for her well-being following her medical leave of absence.

Tanner is a fellow graduate student in Joanna's bird ecology program. He had a brief romantic relationship with Joanna before her cancer diagnosis. He occasionally demonstrates insensitivity regarding her illness and physical changes, causing friction when they interact.

George Kinney is the long-time neighbor of the Nash family who owns the land where Joanna's cottage is located. He works at the nearby college and has maintained a decades-long friendship with Katherine Nash and her late husband.

Frances is a landlady looking to immediately lease her property so she can move out of state to care for her injured former partner. She has strict rules against children and dogs but agrees to rent the house to Joanna and Tabby.