Nine days earlier, Susan, an exhausted teacher on maternity leave, sits pinned beneath her four-month-old daughter, Bella, missing her pre-baby independence. Having struggled with postpartum depression after Bella’s birth, she worries about relapsing.

On the Oakpark neighborhood WhatsApp group, Susan thanks her neighbor Celeste Geary for posting information about the upcoming summer party. Celeste posts another message criticizing people who thank others needlessly in WhatsApp groups. She pointedly states that this is a time-wasting exercise for busy people like herself. Susan takes this as a personal attack, takes a screenshot, and drafts a furious rant intended only for her sisters. She notes that Celeste’s husband was seen with the public-relations (PR) woman at Bar Four; that Celeste’s “bratty” daughter, 17-year-old Nika Geary, skips school to see her boyfriend; and that Celeste covered up a babysitting incident involving her son, 15-year-old Cody, and a neighbor’s toddler. Susan inadvertently posts the message, with the screenshot, to the entire group, oblivious to her mistake. Susan’s husband, Jon Mullane, arrives home just as her sister Greta calls frantically to alert her to the mistake. Susan deletes the message, but dozens of residents have already seen it.

Susan’s message spreads rapidly through Oakpark. In the 10 minutes before she deleted it, dozens of residents screenshot it and forward it to other groups. Replies flood the Oakpark chat—some demanding to know who “SO’D” is. Susan’s display name and her daisy profile picture offer partial anonymity, but she knows it won’t last.

Jon tries to comfort Susan, who’s consumed by guilt for mentioning Celeste’s teenage children since she’s their teacher. Jon suggests that she call Celeste to apologize. Susan tries calling twice but gets no answer and then leaves the WhatsApp group. Direct messages pour in from strangers calling Susan a “disgrace.” After midnight, as she lies awake, a crash sounds from inside the bedroom.

A brick smashes through the bedroom window, narrowly missing Bella’s crib. Susan grabs the baby and checks her for injuries while Jon inspects the damage. They hear a car leaving but see nothing on the Ring doorbell footage. Jon calls the police and is given an email address for further reports. Susan takes Bella to the guest room, unable to sleep.

On Wednesday morning, Jon offers to stay home—a gesture prompted by their recent marriage-counseling sessions, which they keep secret from Susan’s sisters. Susan declines, as Greta is coming over. Greta lives next door in their modernized childhood home. As she and Greta sit at the kitchen table waiting for the glazier, Susan checks her phone and finds six hostile messages. The doorbell rings, and it’s not the glazier but their neighbor Juliette Sullivan, who arrives under the pretense of concern but clearly relishes the drama. Back in the kitchen, Greta shows Susan her phone, saying she needs to see something.

Greta reveals that someone in a local Facebook group has doxxed Susan, sharing her phone number and address and suggesting that people email her school principal. Susan is horrified. Later, a delivery arrives addressed to Savannah Holmes. Savannah’s packages from high-end stores are frequently misdelivered to Susan since their addresses—26 Oakpark—are identical, although Savannah lives on another estate of the same name near Loughlinstown. Susan reveals that she’s been following Savannah on Instagram, fascinated by her glamorous, child-free life. As they scroll through Savannah’s account, Susan remembers that Nika Geary, Celeste’s daughter, has a tree-nut allergy—the same condition that Savannah posts about. Greta starts to mention something else about Nika but stops herself, saying she’ll explain later. After Greta leaves, Susan receives an anonymous text: “IT SHOULD HAVE BEEN YOU” (259). She remembers that she has a counseling appointment and forces herself to go.

Susan drops Bella off with her other sister, Leesa, and attends her counseling appointment. Afterward, emotionally drained, she walks home past Celeste’s house, hoping for some sign of forgiveness. The house is shuttered and empty. While approaching her own driveway, she feels watched and is startled by the glazier arriving to fix the window.

Later, Susan recalls Greta’s unfinished comment about Nika. She searches online and finds a primary-school graduation photo suggesting that Leesa’s 17-year-old daughter Maeve Khoury was once friends with Nika. That evening, Greta and Leesa visit. When pressed, Greta reveals that Nika was part of the group that bullied Maeve at school. Leesa confirms that she kept this from Susan to protect her from losing impartiality as Nika’s teacher. Susan then receives a Google Alert announcing her own death. The post claims that she was found murdered in Oakpark.

Susan realizes that the Google Alert stems from confusion between the two Oakparks. Greta confirms that the story is real—three bodies have been found across two South Dublin locations. The radio news identifies the Oakpark victim as Savannah Holmes, the woman whose packages Susan has been receiving. The personal connection shakes Susan. More details emerge online: Savannah’s body was found by a courier who had peered through her blinds. Leesa points out that the courier may have been collecting a misdelivered package meant for Susan. She then voices a theory: Savannah, a dark-haired woman of similar build living at the same address, may have been killed by someone who mistook her for Susan.

Thirty-six hours before the present timeline, Savannah Holmes followed her disciplined routine—early workout, protein shake, work by seven. She opened packages, including silver ballet flats that she filmed for Instagram, and discovered a Cult Beauty retinol order that belonged to someone else. Her Sézane jumpsuit had been misdelivered to the other Oakpark again.

Savannah reflected on her ex-husband’s upcoming remarriage and her difficult relationship with her mother. At lunch, she was annoyed to discover a grocery substitution contained traces of nuts. By mid-afternoon, she was drinking white wine in the garden, unaware she had less than a day to live.

Susan goes to Blackrock garda (police) station with Leesa to report her theory that Savannah was killed by mistake. The officer is skeptical but listens as Susan lays out the evidence and agrees to investigate. Back home, Susan fills Jon in on everything, and he’s visibly shaken. Susan texts Celeste a lengthy apology, raising the possibility that the murder may be connected to her viral message.

Celeste reads Susan’s text with contempt, interpreting it as an insinuation that she or someone in her circle committed murder. She examines her skin in the mirror, privately maintaining the fiction that she’s five years younger than her actual age of 50.

Downstairs, her husband, Warren, attempts to apologize for his infidelity. Celeste responds coldly. Although he’s been unfaithful before, this is the first time an affair has publicly humiliated her. Celeste then decides to call Susan back.

Celeste rejects Susan’s offer to apologize to her children and husband in person. She demands a public apology online, in which Susan claims she fabricated everything. Susan nearly protests that the message was true but catches herself and agrees. After hanging up, Jon reassures her that Celeste can’t force a public retraction. Susan reflects on her counselor’s advice about intrusive thoughts—the terrifying postpartum fear that she might hurt Bella. She checks the baby monitor, goes upstairs to look at Bella, and notices the plywood-boarded window, feeling unnerved by her inability to see outside.

Susan’s niece Maeve sees the screenshot circulating on Snapchat and is embarrassed by her aunt’s behavior. The chapter then flashes back to an incident on Junior Cert results day. One of Nika’s friends smuggled in a bottle of vodka that broke on the corridor floor. Maeve slipped in the spill, drawing the vice principal’s attention to Nika and her friend’s misdemeanor. The girls blamed Maeve when they got in trouble and bullied her relentlessly through Transition Year and into fifth year—spreading rumors, ostracizing her, and posting about her online. After Maeve’s best friend moved to Spain, the isolation worsened.

Back in the present, Maeve notices that the online conversation has shifted from Susan’s mistake to a new question: Nika doesn’t have a boyfriend, so who is she secretly seeing?

On Thursday morning, Greta and Leesa arrive with coffee and croissants. Susan’s phone rings with a call from Detective Kellerman, who asks Susan to come to the station the following morning for further questions. Leesa interprets this as confirmation that the police are seriously considering a connection to Susan’s message. Susan then recounts the Bar Four opening in detail: how she met Warren Geary; chatted with PR woman Aimee Quinlan and her bartender sister, Venetia; and later stumbled into a storeroom where she caught Warren and Aimee in a compromising embrace. She left unnoticed.

Leesa and Greta discuss who might be behind the threats. Susan notes that she didn’t use Aimee’s name in the message but included enough detail to identify her. Leesa proposes visiting Bar Four to speak with Venetia and track down Aimee’s surname. At the bar, a colleague reveals that Venetia is off work because of a bereavement—Aimee and her husband, Rory, are the murdered couple from Cherrywood. Susan is stunned. The barman directs them to Venetia’s cottage. They walk past, but Susan doesn’t knock on the door, wanting to stay out of the spotlight.

That evening, Susan tells Greta and Jon about Aimee’s death. She worries that both Savannah and Aimee were killed because of her message, making her the link between the two crime scenes.

Nika lies on her bed, furious about Susan’s message. She’s embarrassed by being called “bratty,” resentful that her father’s infidelity has been made public, and worried about the mention of her “boyfriend.” She knows that people will soon figure out the boy is Zach, who is actually her friend Ariana’s boyfriend. Despite being rattled, Nika is confident that her mother won’t question the school-skipping claim. Celeste mostly leaves her alone, and Nika does exactly as she pleases.

At 3:11 am on Friday, Susan is jolted awake by a threatening text from the same untraceable number: “Lock your doors, Susan […] I’m the monster outside right now. Watching” (66). She wakes Jon, and they peer out the nursery window but see only a fox. Jon calls the police, who send a car and confirm that no one is outside. In bed afterward, Susan fixates on a phrase in the message—“I told you, if you tell anyone, I’ll be back” (67)—which doesn’t make sense, as no one has told her anything. She senses that this anomaly is the key to understanding who’s behind the threats.

On Friday morning, Detective Kellerman asks Susan to come to the garda station. Kellerman reveals that the threatening texts came from an untraceable prepaid phone. She goes through Susan’s connections to the victims and then discloses that Savannah’s murder was not a burglary. Her car keys were missing, but not the car itself. The detective asks if Susan knows anyone named “Sam” and requests DNA and fingerprints for exclusion purposes. Susan learns that unidentified forensic evidence was found at both crime scenes and that, so far, she’s the only “common denominator” linking the Cherrywood and Oakpark murders.

Back at home, Susan is exhausted but can’t sleep. She searches for Jon’s melatonin supplements in his bedside drawer and finds a rose-gold bracelet hidden behind the bedside cabinet. Engraved on the inside is a romantic message celebrating Jon’s “one-month anniversary” with another woman (73). 

Susan agonizes over the bracelet. She checks the joint credit card and finds a charge from the Marker Hotel—the cost of two drinks. She mentally catalogs Jon’s recent behavioral changes: working late, overnight trips, and the sudden obsession with running as a perfect cover for secret meetings. She considers telling her sisters but fears that disclosure would force a confrontation she isn’t ready for. She also dreads that Jon might use her postpartum mental-health struggles against her in a custody battle. Jon is the only person outside her medical team who knows about her intrusive thoughts of hurting Bella.

On Friday evening, Susan hides her anguish behind her sisters’ noisy presence. She notices Greta and Jon exchange a glance and wonders if Greta knows about the affair. Jon pours wine and notices Greta’s naltrexone, a prescription medication for long COVID that reduces alcohol’s effects. He jokes about using it for client drinks and driving home. Susan finds the comments insensitive, given Greta’s limp from a car accident years earlier. In the living room, Susan catches Leesa’s daughters, Maeve and 13-year-old Aoife, huddled over a Snapchat group full of hostile posts about Nika. Aoife explains that Nika’s secret boyfriend is Zach, the boyfriend of Nika’s friend Ariana.

Over takeout and wine, Susan shares the Zach-Nika-Ariana love triangle with the group. Jon asks whether the social media pile-on gives Nika a motive for the threats and broken window. Susan concedes that the early incidents are plausible, but she can’t believe a teenager committed the murders. Greta, still angry on Maeve’s behalf, says that Nika deserves “a taste of her own medicine” (86). Maeve muses aloud that it would be useful if there were a medicine to either “fix people […] or get rid of them” (86).

On Saturday morning, Celeste watches Warren nervously prepare to confess something. He reveals that the police want a statement about the Bar Four incident and that Cody’s work-experience placement has been rescinded because the company learned about the babysitting incident with the neighbor’s toddler. Celeste blames Warren: Had he not cheated, Susan’s message would never have been sent, and none of this would have happened. Cody arrives, learns that his placement is gone, and storms upstairs.