Jack is a fourteen-year-old boy living in a cramped city apartment. He suffers from a severe allergy to sunlight that forces him to stay indoors during the day and rely on a special protective lotion. Frustrated by his physical limitations and his parents' recent separation, he finds his only freedom by jumping between shadows on neighborhood rooftops.

Beth is a teenager who recently moved to Jack's city after her parents died in a car crash. She deliberately wears heavy gothic makeup to project an intimidating exterior and discourage people from asking about her past. She carries a heavy black rucksack at all times and protects it fiercely from anyone who tries to touch it.

Maeve is Jack's hardworking mother who struggles to support her son following her recent separation from her husband. She works long retail hours to afford their small apartment in the city. Her exhaustion and financial stress make it difficult for her to closely monitor Jack's physical condition.

Tom is a brilliant but emotionally volatile research scientist. He previously worked at Bioscience Discoveries, where he helped develop the special lotion Jack uses for his sun allergy. He recently left his family and cut off contact, leaving behind unanswered questions about his work.

Auntie Lil is Tom's sister, described as short and round in contrast to her tall brother. She lives in the smaller town of Colford and serves as the family's main point of contact with Tom.

Mrs. Roberts is an elderly, hard-of-hearing woman who lives in the apartment next door to Jack and Maeve. She frequently checks on Jack at Maeve's request, a habit that Jack resents and interprets as intrusive.

Kai is a large, muscular older teenager who dominates parts of the city's rooftops. With a broad-shouldered frame and a menacing demeanor, he acts aggressively toward anyone who encroaches on what he considers his territory.

Cathy is a family friend of Beth's late parents who steps in as her guardian. She lives in a large house with a sizable garden and raises seven children of her own, making the household loud and chaotic.

Pete is Cathy's partner and Beth's co-guardian. Together with Cathy, he provides a home for Beth following the tragic death of her parents.

Mia is one of Cathy and Pete's seven children. She shares a bedroom with Beth in their large house and routinely takes Beth's belongings without permission.

Ted is a former cleaner at Bioscience Discoveries with an unkempt appearance and a lingering odor. He acts as a whistleblower, eagerly sharing disturbing rumors about unethical experiments at his former workplace.

Fiona is the public relations manager at Bioscience Discoveries. She presents a professional exterior but becomes visibly suspicious and cold when visitors ask probing questions about the company's past scandals.

Dr. Richard Blackstone is the director of Bioscience Discoveries in Colford. He oversees the facility where Tom previously worked on anti-aging experiments and maintains strict security protocols around his private laboratories.

Rex is a Labrador dog found near Colford. He is discovered missing patches of hair and covered in painful-looking sores, a condition that immediately reminds Jack of his own severe skin allergies.