Willow is an exceptionally bright kindergarten student living with Type III osteogenesis imperfecta, a rare genetic disorder that causes her bones to break with minimal impact. She reads at a sixth-grade level, loves watching Jeopardy!, and frequently recites trivia to connect with those around her. Despite her fragile physical state and small stature, she strives for independence and deeply dislikes being treated like a toddler.

Charlotte is a devoted mother and former pastry chef who frequently expresses her affection by baking intricate desserts. She acts as a hyper-vigilant caregiver for her youngest daughter, managing constant medical emergencies and the resulting financial strain on her family. Her intense focus on Willow leaves little room for her own career aspirations or her older daughter's needs. She initiates a controversial medical malpractice lawsuit to secure a financial safety net for Willow.

Sean is a police officer in New Hampshire who struggles to communicate his emotions effectively. He relies heavily on his professional authority when he feels powerless in his personal life, especially regarding his inability to financially cover Willow's expensive medical care. His approach to parenting involves more risk-taking than his wife's, but he frequently turns to physical outbursts when frustrated by his family's chaotic circumstances.

Amelia is Charlotte's 13-year-old daughter who feels completely invisible in a household revolving around her sister's medical emergencies. She uses sarcasm to deflect attention from her internal struggles and loneliness. Left without adequate emotional support, she develops an eating disorder and begins shoplifting as ways to exert control over her turbulent life.

Piper is a successful obstetrician-gynecologist whose career defines much of her identity. She enjoys a comfortable, affluent lifestyle that contrasts sharply with the O'Keefe family's financial struggles. Following the filing of the lawsuit, she steps away from her medical practice and throws herself into obsessive home renovation projects to cope with the destruction of her closest friendship.

Marin is a 35-year-old attorney working for Robert Ramirez. She is highly career-driven and struggles to separate her personal biases from the O'Keefe case. As an adopted child currently searching for her biological origins, she finds the concept of a wrongful birth lawsuit personally offensive, though she remains professional enough to represent Charlotte.

Rob is an orthodontist and Piper's husband. He prioritizes his practice and reputation in their small town, showing frustration when Piper's legal troubles threaten to cost him patients. He eventually recognizes the toll the situation takes on his family and attempts to offer support.

Emma is Piper and Rob's teenage daughter. She enjoys a comfortable life and frequently shares clothes and secrets with Amelia. Her loyalty strictly aligns with her mother once the legal battle begins, resulting in her turning against her former best friend.

Guy is a medical malpractice defense attorney representing Piper. He is aggressive in his legal strategies and completely focused on winning, viewing the emotional complexities of the O'Keefe family merely as tools to manipulate a jury.

Robert is a plaintiff's attorney who first identifies the potential for a wrongful birth lawsuit in Charlotte's medical records. He focuses heavily on the financial payout potential and delegates much of the trial preparation to Marin.

Juliet is a local woman called for jury duty in the medical malpractice trial. She reacts emotionally to the case's subject matter and specifically asks to be dismissed from serving due to the sensitive nature of the trial arguments.

Adam is a teenager who attends the 2008 Biennial Osteogenesis Imperfecta Convention. He reads OI blogs and recognizes Amelia when she attempts to pass herself off as a patient.

Father Grady is a local Catholic priest. Despite his own moral failings, he continues to counsel his parishioners and discourages divorce within the community.

Maisie is a courthouse employee who assists with pulling adoption decrees and legal records.