Grace's husband, a 40-year-old lawyer known for defending battered women. He is charming and polite in public, concealing a darker side that becomes central to the story.

Grace's 18-year-old sister with Down Syndrome, who enjoys trips to Regent’s Park and spending time with Grace. She plays a significant role in Grace's life and her decision-making.

A new friend introduced through a connection at a dinner party, who is insightful and perceptive regarding her observations of Jack and Grace's life together.

Millie’s aide at the private school, who is dedicated to Millie's care and spends most of each day with her. She remains unaware of Grace's personal struggles for much of the story.

Jack's colleague at the law firm and a supportive friend. He becomes involved when Grace reaches out for help under distressing circumstances.

Adam's wife, who has known Grace and Jack for a long time and often comments on Grace's seemingly ideal life, while balancing her own personal struggles.

The director of Millie’s school, known for making key decisions in Millie’s education and care. She provides advice regarding Millie's well-being.

Esther’s husband and a musician. He is portrayed as good-natured and supports Esther and their children.

Grace and Millie’s parents, who distanced themselves from parental responsibilities early on, especially after Millie's birth.

The hotel manager at the hotel in Thailand frequented by Grace and Jack. He is professional and diligent in his role.

The concierge at the hotel in Thailand, initially helpful to Grace but later shown to defer to Jack’s authority.

A couple Grace meets during a vacation in Thailand, offering friendship and support during a challenging time.