Susan is a secondary-school teacher currently on maternity leave in the affluent South Dublin suburb of Oakpark. Struggling with sleep deprivation and postpartum anxiety, she feels isolated from her pre-baby life and judged by her wealthy neighbors. When she accidentally sends a mean-spirited rant about a neighbor to a 300-member community WhatsApp group instead of her sisters, she triggers a severe local backlash. She relies heavily on her sisters for support while trying to process the sudden influx of hostility and alarming threats directed at her home.

Greta is Susan's pragmatic and protective older sister who lives next door in their modernized childhood home. Working as a local hockey coach, she maintains a calm, stoic exterior that grounds Susan during stressful periods. She walks with a permanent limp from a past car accident and strictly guards her family against perceived threats, taking on a maternal role following their mother's early death.

Jon is Susan's husband, presenting himself as an easygoing partner who frequently goes for long runs to decompress. He is the only person outside of Susan's medical team who knows about her postpartum intrusive thoughts, giving him a unique level of insight into her mental state. As the neighborhood fallout escalates, his anxious behavior, sudden late working hours, and hidden belongings introduce tension into their household.

Venetia is a bartender who lives in a modest cottage in Coal Place. She is fiercely protective of her sister Aimee and holds deep resentments against Aimee's abusive husband. Following a tragic bereavement, she becomes volatile and fixated on the people she blames for upending her life, deciding to seek aggressive retribution.

Celeste is a high-powered, 50-year-old banker living in Oakpark who is obsessed with maintaining a flawless public image. She treats her family's reputation as an extension of her personal brand and reacts coldly to public embarrassment. When Susan's text exposes her husband's infidelity and her children's misbehavior, she focuses entirely on managing the scandal rather than addressing the root issues in her home.

Nika is Celeste and Warren's 17-year-old daughter. Polished but rebellious, she secretly dates her friend's boyfriend and deals with complex teenage social hierarchies. When Susan's text exposes her secrets, she faces intense cyberbullying from her peers and responds with calculated digital retaliation. She lives with a severe tree-nut allergy that requires constant vigilance.

Felipe is Venetia's gentle and protective husband. Originally entering a marriage of convenience for visa purposes, he has developed genuine care for his wife. He attempts to manage Venetia's emotional instability while carrying his own profound guilt regarding the recent violent events in their social circle.

Maeve is Leesa's 17-year-old daughter and Susan's niece. A quiet teenager, she previously suffered severe bullying orchestrated by Nika after a school incident. She remains highly sensitive to social dynamics and feels profound shame when her private childhood secrets are weaponized online.

Savannah is a wealthy, single woman who lives at an identical address to Susan in a different part of the Oakpark suburb. She leads a glamorous, child-free life documented on Instagram, which Susan secretly envies. Her sudden death initiates the central mystery of mistaken identity in the neighborhood.

Leesa is Susan and Greta's sister, a busy mother who lives nearby in the suburbs. She frequently acts as a sounding board for Susan's anxieties and is the first to theorize that Savannah Holmes might have been killed by an intruder who went to the wrong house.

Warren is Celeste's husband, whose persistent infidelity finally becomes public knowledge due to Susan's text message. His lack of discretion causes immense strain within his family and jeopardizes their carefully maintained social standing in Oakpark.

Cody is Celeste and Warren's 15-year-old son. He struggles with feelings of inadequacy and a troubled reputation after endangering a neighbor's toddler. The fallout from the text message costs him a work-experience placement, worsening his emotional distress and self-destructive habits.

Aimee is a public relations representative and Venetia's sister. She is trapped in an abusive marriage with her husband, Rory, and becomes the subject of neighborhood rumors regarding an affair with Warren Geary, directly resulting from Susan's viral message.

Rory is Aimee's husband. He has a history of domestic abuse and volatile behavior, creating a dangerous living situation for Aimee that deeply concerns her sister, Venetia. His violent temper is easily provoked by rumors and slights.

Aoife is Leesa's 13-year-old daughter. She is observant and deeply curious about the neighborhood drama, often hovering outside doors to eavesdrop on conversations and attempting to comfort her older sister Maeve when she is upset.

Bella is Susan and Jon's four-month-old daughter. She is entirely dependent on her parents and unwittingly becomes a target for those seeking to terrorize Susan. Her safety is the primary motivation for many of Susan's actions.

Juliette is an intrusive neighbor in Oakpark who relishes local gossip and drama. She masks her snooping and judgment with superficial concern, adding to Susan's feelings of isolation and fear regarding child-welfare rumors.

Kellerman is the police detective assigned to investigate the murders connected to Oakpark and Cherrywood. He pieces together the forensic evidence and questions the neighborhood residents, identifying Susan as the central link between the different crime scenes.

Albie is a local politician and Savannah's ex-husband. He frequently appears in the press and is connected to a past car accident involving Greta. Jon uses his name to misdirect police attention away from himself.