A 27-year-old childcare worker from London who accepts a highly paid residential nanny position at the remote Heatherbrae House in the Scottish Highlands. Currently imprisoned and awaiting trial, she writes letters to explain the events leading to her incarceration. She presents herself as competent and eager but struggles with the demanding realities of her new job and the home's unsettling atmosphere.

The matriarch of the Elincourt family and co-owner of a successful vernacular architecture firm. She is a thin, blonde woman in her forties who relies heavily on nannies to manage her four daughters while she travels for business. Though she provides thorough instructions and a technologically advanced home, her frequent absences create a challenging environment for her employees.

The patriarch of Heatherbrae House and an architect who runs a firm with his wife. He is a tall, tanned man who enjoys the financial comforts of his successful career. He travels often for work and leaves the childcare primarily to his wife and their hired staff, maintaining a distant but imposing presence in the household.

The eight-year-old daughter of the Elincourt family. She has dark hair and a sallow complexion, contrasting visually with her blonde sisters. She is highly resistant to new nannies and acts stubbornly, using her knowledge of the property to intimidate newcomers.

The five-year-old daughter of the Elincourt family. She has blonde hair and blue eyes, and she initially appears friendlier than her older sister. Despite her young age, she is deeply affected by the high turnover of nannies and her parents' frequent absences.

The eighteen-month-old baby of the Elincourt family. She is entirely dependent on the household's nanny for her daily care, feeding, and routine.

The fourteen-year-old eldest daughter of the Elincourt family who attends a boarding school. She possesses a rebellious, aloof attitude and clashes with authority figures. She maintains a surly distance from the household's staff and deeply resents the disruption in her family life.

The resident odd-job man and groundskeeper at Heatherbrae House. He is a young, handsome man with a Scottish accent who assists with the property's upkeep and the family's dogs. He offers guidance and friendly support to the newly arrived nanny as she struggles to adjust to the isolated estate.

A woman in her fifties who works mornings as an employee at Heatherbrae House, assisting with the children's school routines. She spends her afternoons in the nearby village caring for her ailing father. She is deeply protective of the Elincourt children and initially views new staff members with suspicion.

The mother of the narrator. She is remembered as a cold and dismissive parent who frequently criticized her child. She eventually moves to Spain to retire, deepening the emotional distance between her and her daughter.

The former owner of the estate back when it was known as Struan House. He was an analytical chemist who cultivated a dangerous poison garden on the property. Local legends and ghost stories about him and his tragic family history continue to haunt the current residents.

A solicitor known for helping desperate clients in difficult legal situations. He is the intended recipient of a lengthy correspondence from prison, serving as the silent audience for the story of what happened at Heatherbrae House.