Grace is a woman in her early thirties who recently gave up her career as a fruit buyer for Harrods to marry Jack. She serves as the sole guardian for her younger sister, Millie, and structures her life around ensuring Millie's well-being. Although she appears to enjoy a life of luxury in Surrey, she harbors intense anxiety and carefully moderates her behavior around her husband.

Jack is a forty-year-old attorney who specializes in prosecuting men who abuse their wives. He presents himself to the world as an exceptionally handsome and highly attentive partner who dotes on Grace. Behind the closed doors of their home, this charming exterior masks an obsessive need for control over his household.

Millie is Grace's eighteen-year-old sister who has Down Syndrome and attends a private residential school. She loves the color yellow and frequently listens to Agatha Christie mysteries on audiobook. She possesses a sharp intuition about people and often notices behavioral cues that others miss entirely.

Esther is a tall, fair-haired woman who recently moved to the suburb of Spring Eaton. She is inquisitive and sharp, frequently asking pointed questions about Grace and Jack's seemingly ideal lifestyle. Her probing nature makes her stand out among the couple's otherwise compliant social circle.

Janice is a dedicated caregiver at the private boarding school Millie attends. She spends much of her day with Millie and acts as a consistent, nurturing presence in her daily routine. She maintains a professional, polite rapport with Grace and Jack regarding Millie's care.

Adam is a lawyer and one of Jack's oldest friends. He respects Jack's professional abilities and views him as an exemplary attorney, fully buying into the polished image his friend presents to the world.

Diane is a dark-haired working mother who has known Jack for years through her husband. She frequently compares her chaotic daily schedule with Grace's stay-at-home existence, occasionally allowing feelings of jealousy to surface during their interactions.

Mrs. Goodrich is the director of the private boarding school where Millie resides. She oversees the educational needs of the students and coordinates with family members regarding any behavioral or health concerns.

Rufus is a working musician. He is a good-natured individual who accompanies his wife to social events in their new neighborhood, bringing a relaxed presence to formal dinners.

The Harringtons are Grace and Millie's parents, who never truly wanted children. They gladly relinquished the primary care of Millie to Grace and focus instead on their own plans to retire abroad.

Mr. Ho is the hardworking manager of the hotel where Grace and Jack spend their honeymoon in Thailand. He is highly attentive to the needs of his guests and relies heavily on Jack's explanations when conflicts arise.

Kiko is a receptionist at the Thailand hotel who assists guests with their requests. She tries to be accommodating but ultimately defers to her manager during unusual situations.

Margaret and Richard are a married couple vacationing in Thailand. They are friendly and sociable, offering polite company and conversation during an overnight tour.