Tessa is a sixteen-year-old British girl living with terminal leukemia. Frustrated by her fading health and the dreary constraints of her treatment, she creates a secret list of rebellious acts she wants to experience, from having sex to breaking the law. She is fiercely independent, often pushing away the people who care for her, yet desperately yearns to live a normal teenage life.

Dad is Tessa's devoted and exhausted primary caretaker. He is patient, hardworking, and deeply protective, shouldering the immense burden of managing his daughter's illness and his household alone. His constant vigilance often frustrates Tessa, who sees his care as a reminder of her fading health.

Mum is an adventurous, wealthy-born woman who left the family when Tessa was twelve. She has recently moved back into a nearby apartment following the news of Tessa's diagnosis. She possesses a charming, impulsive spirit that entertains Tessa, but she severely lacks the reliability and practical skills needed for caretaking.

Cal is Tessa's younger brother. He struggles to fully comprehend the gravity of his sister's illness, often using dark humor and blunt comments to cope with the tension in the house. Despite their typical sibling bickering, he forms a crucial part of Tessa's grounding reality.

Zoey is Tessa's best friend, known for her wild, rebellious, and fiercely independent streak. She dresses Tessa up, sneaks her into clubs, and encourages her rule-breaking desires. Beneath her party-girl exterior, Zoey longs for stability and love, often seeking it through reckless romantic entanglements.

Adam is the quiet, slightly disheveled boy who lives next door to Tessa. He spends most of his time doing yard work and caring for his depressed mother following a family tragedy. His status as a solitary outcast draws Tessa to him, providing a calm contrast to her chaotic life.

Sally is Adam's mother. Following the sudden death of her husband in a car accident, she became deeply depressed and reclusive. She relies heavily on her son to manage the household and act as her buffer against the outside world.

Jake is a local boy whom Tessa and Zoey meet during a night out. He provides Tessa with her first sexual experience, though he proves to be oblivious and uncommunicative regarding her emotional distress and physical condition.

Scott is Jake's friend and roommate who runs a market stall. He briefly dates Zoey after the group meets at a club, pursuing a fast-paced romantic connection with her.

Philippa is a home-care nurse assigned to monitor Tessa's deteriorating condition. She maintains a strict, no-nonsense professional demeanor, often clashing with Tessa's cynical and rebellious moods.

Shirley is a stern supermarket detective who catches Tessa stealing. She remains entirely unmoved by Tessa's attempts to use her illness to gain sympathy, insisting on calling Tessa's father instead.

Richard Green is a popular radio host whom Dad contacts to help fulfill Tessa's wish for fame. Despite his public persona, he is a rumpled, impatient man who quickly cuts the interview short when Tessa deviates from the script.