Emma is a vulnerable young woman who applies to live in the austere One Folgate Street after a home invasion. She seeks a sense of safety and control in the highly regulated architectural space. Her time in the house is marked by her turbulent relationship with her boyfriend and her growing fascination with the building's demanding creator.

Jane is an organized woman recovering from the tragic stillbirth of her daughter, Isabel. She moves into One Folgate Street seeking a fresh start and finds comfort in its minimalist austerity. As she settles in, she begins investigating the mysterious fate of the previous tenant, who bore a striking physical resemblance to her.

Edward is a wealthy, brilliant architect who designed One Folgate Street following the tragic deaths of his wife and child. He maintains strict control over his environments and follows scripted patterns in his romantic relationships. His commanding presence draws both Emma and Jane into his orbit as he tests their willingness to conform to his rules.

Simon is Emma's boyfriend, a magazine writer who works in a boozy, male-dominated environment. He moves into One Folgate Street with Emma but struggles to adapt to both the house's strict rules and the aftermath of Emma's trauma. His behavior oscillates between emotional pleading and aggressive frustration as their relationship deteriorates.

Detective Inspector Clarke is a well-intentioned police officer assigned to investigate the violent robbery Emma experienced. He tries to support Emma through the legal process, though the shifting facts of her case present professional challenges. Later, he serves as a source of information for Jane during her investigation.

Carol is an accredited psychotherapist who treats Emma following her traumatic experiences. She attempts to guide Emma toward healthy boundaries while analyzing her behavioral patterns. Later, she becomes a resource for Jane, offering psychoanalytic perspectives on the repetitive actions of the people involved with One Folgate Street.

Saul is Emma's coworker and a close friend to Simon. He is described as pushy, brash, and loud, fitting into the "laddish" culture of his workplace. He acts as an aging lothario who plays a complicated role in Emma's social circle and workplace dynamics.

Dr. Gifford is the medical professional who managed Jane's first pregnancy and was involved in the tragic outcome. He faces institutional scrutiny and mediation regarding Jane's stillbirth, yet Jane must interact with him as she seeks answers and future medical care.

Deon is the intruder who robbed Emma at knifepoint in her previous apartment. His violent actions catalyze Emma's desire to move to the highly secure One Folgate Street, and the subsequent legal proceedings against him add immense stress to her new living situation.

Housekeeper is the advanced technological intelligence system that runs One Folgate Street. It regulates everything from water temperature to lighting, while collecting detailed psychological and behavioral data from the tenants through frequent surveys and mandatory questionnaires.

Mia is Jane's friend who helps her uncover initial details about Emma Matthews and Edward Monkford's past. She acts as a sounding board and a voice of caution as Jane becomes more entangled with the house and its controlling architect.

David is Edward Monkford's technology partner at The Monkford Partnership. He manages the complex software, surveillance cameras, and data collection systems that power One Folgate Street's advanced interface, defending the system's privacy boundaries.

Amanda is Emma's coworker and previous friend, who is married to Saul Aksoy. Her friendship with Emma deteriorates severely due to workplace tensions and personal conflicts involving their partners.

Tessa is Jane's coworker at the Still Hope charity, an organization dedicated to reducing stillbirths. She provides Jane with practical support and firm advocacy advice during difficult mediation sessions with the hospital following Jane's own tragedy.

Elizabeth is Edward Monkford's deceased wife, who died alongside their son in a tragic accident prior to the construction of One Folgate Street. Her distinct physical resemblance to both Emma and Jane establishes a haunting pattern in Edward's romantic life.

Isabel is Jane Cavendish's deceased infant daughter. The profound grief of her stillbirth motivates Jane's desire for a fresh start at One Folgate Street and influences her interactions with medical professionals.