Libby is a 25-year-old woman living in a modest apartment in St. Albans. She works as the head of sales for an upscale kitchen design company and values predictability and order. After receiving an inheritance letter, she discovers her birth name is Serenity Lamb and begins investigating the dark history of her newly acquired house.

Lucy is a homeless woman nearing forty who travels across the Côte d'Azur with her two young children and dog. She survives by busking with a fiddle and relies on fake identification to evade her abusive ex-husband. Despite her extreme poverty, she fiercely protects her children and harbors a desperate desire to return to England.

Henry is an eleven-year-old boy living in a massive Chelsea mansion before his family loses their fortune. When his parents allow strangers to move into their home, he acutely observes the shifting power dynamics and his family's rapid decline in status. Guarded and observant, he harbors intense resentment toward the interlopers controlling his life.

David arrives at the Chelsea mansion as an alternative medicine practitioner. Charismatic and domineering, he quickly charms the residents and implements strict, ascetic rules. He gradually seizes control of the household finances, forcing the family to give up their belongings and adhere to a restrictive, isolated lifestyle.

Birdie is an eccentric fiddle player for a pop band who initially uses the mansion for a video shoot but soon manipulates her way into moving in permanently. She wears oversized men's clothing and heavily supports David's controlling methods, helping enforce his bizarre rules upon the children.

Phin is a strikingly handsome teenager who moves into the mansion with his family. Having been homeschooled and frequently uprooted, he possesses a rebellious, cynical attitude toward his father's authority. He forms a close, complicated bond with Henry while trapped in the house.

Miller is a dedicated journalist who spent years investigating the tragic deaths at the Chelsea mansion. His obsession with the unsolved case previously cost him his marriage, but he proves to be an eager, spontaneous, and helpful ally to Libby in her quest for answers.

Martina is a formerly wealthy socialite of German and Turkish descent who enjoys fashion and shopping. Unhappy with her superficial lifestyle, she easily falls under David's charismatic spell, eagerly surrendering her family's wealth and independence in pursuit of what she believes is a freer, less selfish existence.

Henry Lamb is the wealthy patriarch who inherited his fortune from his father's slot machine business. Following a minor stroke, his physical and mental health decline rapidly, leaving him passive and unable to stop David from usurping his role as the head of the household.

Justin is Birdie's partner and a former percussionist in her band. He plants a large medicinal herb garden in the mansion's backyard to earn money. He eventually distances himself from the household's growing extremism and teaches young Henry about gardening and plant properties.

Sally is David's wife and a teacher who initially arrives to homeschool the children in the mansion. As her husband's affairs and extremist behaviors escalate, she becomes increasingly marginalized and searches for a way to secure housing for her children away from his influence.

Clemency is the young daughter of David and Sally. Homeschooled and subjected to her father's erratic lifestyle, she endures the increasingly oppressive rules of the household alongside the other children while trapped in the mansion.

Marco is Lucy's clever son who has a talent for languages and art. He is highly observant of his mother's struggles and frustrated by her refusal to share details about her past or their current predicament.

Stella is Lucy's young daughter. Sheltered as much as possible by her mother's fierce protection, she endures their transient lifestyle alongside her brother Marco and the family dog.

Michael is Marco's father and Lucy's ex-husband. He is an abusive, wealthy man who initially charmed Lucy but now uses his money and status to demean her and exert control when she is forced to seek his help for travel documents.

Dido is Libby's coworker at the luxury kitchen design company. Coming from a wealthy background herself, she acts as a sounding board and supportive friend as Libby processes the shock of her inheritance and begins investigating her past.

Giuseppe is the kind owner of The Blue House, a run-down residence with a view of the Mediterranean. He previously covered Lucy's rent when she was struggling and provides her family with a safe, welcoming place to stay.

Fitz is the family dog, named after F. Scott Fitzgerald. He travels everywhere with Lucy, Marco, and Stella, serving as a loyal companion during their period of homelessness.

Mr. Royle is the solicitor of the Lamb estate. He provides Libby with the initial newspaper clippings about her family's dark history and guides her through her first unsettling tour of the empty property.

Samia is Stella's paternal grandmother. She offers limited help to Lucy's family during their homelessness, only allowing her own granddaughter to stay the night in her home to escape the bad weather.

Dénia is Libby's adoptive mother. Described as loving but somewhat chaotic, she emigrated to Spain when Libby was eighteen, leaving her responsible, organized daughter to largely look after herself.