Euphemia "Esme" Lennox is a fiercely independent young woman born to a wealthy British family in colonial India. Her rebellious nature and unique perspective put her at odds with her emotionally distant parents and the rigid society of 1930s Scotland. She struggles to adhere to her family's strict social expectations, preferring the freedom of childhood and the comfort of her nanny. In the present timeline, she faces the closure of Cauldstone, the psychiatric facility where she has resided for over sixty years.

Iris is an independent vintage clothing shop owner living in modern-day Edinburgh. Inheriting her flat from her grandmother, she leads a largely solitary life marked by complicated romantic entanglements and a deep appreciation for history. Her structured reality shifts abruptly when she receives a phone call informing her she is the closest living relative to a great-aunt she never knew existed.

Kathleen "Kitty" Lennox Lockhart is Esme's older sister, a woman who strictly adheres to her family's upper-class social expectations. Groomed to become a proper lady and find a suitable husband, she embraces the conventions of 1930s Scottish society. In the present day, she resides in a nursing home with Alzheimer's disease, her scattered memories offering a fragmented perspective on her family's past.

Alexander is Iris's former stepbrother, a man who maintains a constant, intense presence in her life despite his own marriage. Having bonded with Iris over their fractured home lives during childhood, he frequently returns to her orbit whenever she begins a new relationship. He views her connection to the hospital with deep suspicion and urges her to walk away from the situation.

Ishbel Lennox is a traditional upper-class mother heavily invested in maintaining her family's reputation. Emotionally distant from her children, she focuses her maternal efforts on ensuring her daughters present well in society and secure advantageous marriages. She relies on servants for childcare and struggles to handle her younger daughter's fierce independence.

Mr. Lennox is a strict, traditional patriarch who demands total obedience from his family. Often absent from the daily routines of the household, he steps in primarily to discipline his children when their behavior threatens his social standing. He uproots his family from colonial India back to his homeland of Scotland, expecting his daughters to seamlessly adapt to their new, austere environment.

James Dalziel is a charming, handsome young man who runs in the Lennox family's elite social circles. While he presents the image of a perfect gentleman and a highly desirable match, he harbors a dark, intense fascination with those who resist his charms. He aggressively pursues a connection with the Lennox family, disrupting the sisters' social dynamic.

Luke is a tall, handsome lawyer currently carrying on an affair with Iris. Though he promises to leave his wife to pursue a legitimate relationship with Iris, his actions often reflect a self-centered approach to romance. He shows little interest in Iris's family history and openly criticizes her decision to involve herself in her great-aunt's life.

Jamila is the Lennox family's ayah, working for them during their time in colonial India. She provides the maternal affection and warmth that the children's biological parents lack, creating a safe haven in the nursery. She is deeply devoted to the children under her care, serving as a primary source of comfort.

Hugo is the youngest child of the Lennox family, born while they are living in colonial India. He is a source of immense joy for his older sister, who relishes the opportunity to entertain him and hold him under the watchful eye of their nanny.

Grandmother Lennox is the formidable matriarch of the family who oversees the girls' transition to life in Scotland. She holds extremely strict views on female propriety, actively working to scrub away the girls' Indian upbringing to mold them into proper Scottish ladies.

Duncan Lockhart is a socially acceptable, emotionally reserved man who proposes to Kitty after a brief, unromantic courtship. He works for his father-in-law and values order and routine, counting and polishing the silverware after parties rather than engaging in intimate conversation with his wife.

Robert is Kitty's son and Iris's late father. He dies young at the age of thirty-one due to an allergic reaction to hospital medication. Though deceased before the main events of the present narrative, his memory heavily influences the surviving members of his family.

Peter Lasdun is an administrative representative at the Cauldstone psychiatric hospital. Tasked with the difficult job of finding homes for the facility's long-term residents before the building closes, he serves as the catalyst for a sudden family reunion.

Fran is Alexander's wife, a woman who adheres to conventional aesthetics and societal norms. She maintains a strained, tense dynamic with her husband and feels alienated by the intensely close, private bond he shares with his former stepsister.

Gina is Luke's pregnant wife. She is entirely unaware of his infidelity, representing the collateral damage of a secret affair occurring in modern-day Edinburgh.

Sadie is Iris's mother and Robert's former partner. After Robert's death, she raises Iris and eventually enters a relationship with George, bringing Alexander into their household. She currently resides in Australia.

George is Alexander's father who enters a relationship with Sadie. His relationship with Iris's mother merges the two families, though their eventual separation causes a rift that leads to his son being sent to boarding school.

Mrs. Dalziel is Jamie's mother, a woman entrenched in the high society of Scotland. She facilitates her son's social encounters and protects him after a disastrous New Year's Eve party.

Catriona McFarlane is a cruel schoolgirl who bullies others over their unruly hair and foreign birthplaces. She serves as a primary antagonist in the school setting, escalating her pranks to sabotage her targets.