Andrea Mara’s domestic-noir thriller It Should Have Been You (2025) is set in a wealthy South Dublin suburb where a single digital mistake unleashes a cascade of deadly consequences. The novel follows Susan O’Donnell, a new mother on maternity leave who accidentally sends a gossip-filled text about a neighbor to her entire 300-member neighborhood WhatsApp group. The message’s rapid spread leads to online threats, a home invasion, and murder, forcing Susan to confront the possibility that a case of mistaken identity has led to a stranger’s death. The narrative explores themes of Digital Communication and the Collapse of Privacy, The Unforeseeable Consequences of Small Transgressions, and The Pervasiveness of Deception and Hidden Lives.

An Irish author from Dublin, Mara has established herself as a prominent voice in the thriller genre, with multiple titles becoming Sunday Times and Irish Times bestsellers. Several of her novels have been shortlisted for the Irish Crime Novel of the Year award. Her other books include All Her Fault (2021), which was adapted into a television series; No One Saw a Thing (2023); and Someone in the Attic (2024).

This guide refers to the 2026 Pamela Dorman Books/Viking edition.

Content Warning: The source material and guide feature depictions of graphic violence, death, child abuse, physical abuse, emotional abuse, bullying, mental illness, suicidal ideation and self-harm, pregnancy loss, addiction, and substance use.

Plot Summary

Set in the suburbs of South Dublin, Ireland, the novel opens with a flash-forward: Susan O’Donnell narrates that she must kill her sister Greta O’Donnell by injecting her with heroin. As fireworks from a neighborhood summer party explode outside, Greta collapses to the kitchen floor. Susan reflects that, in the last 10 days, four people have died, a teenager has been hospitalized, another is in police custody, and her family is destroyed—all due to a text message.

Nine days earlier, Susan, a secondary-school teacher on maternity leave with her four-month-old daughter, Bella, is sleep-deprived and struggling with postpartum intrusive thoughts that she has disclosed only to her husband, Jon; her doctor; and her counselor. In a discussion about the upcoming Oakpark summer party on the neighborhood WhatsApp group, Celeste Geary, a high-powered banker, posts a passive-aggressive rebuke targeting Susan. Susan fires off a mean-spirited rant to her two sisters, accompanied by a screenshot of Celeste’s message. Susan’s text references Celeste’s husband, Warren, having an affair with a “PR girl” at a local pub called Bar Four. She also calls the Gearys’ daughter, 17-year-old Nika, “bratty”; mentions Nika skipping school with a boyfriend; and alludes to the Gearys’ son, 15-year-old Cody, covering up a babysitting incident involving a neighbor’s toddler. Susan accidentally sends the message to the entire 300-member group. She deletes it within minutes, but dozens of residents have already taken screenshots, and the message spreads across local social media.

The fallout is immediate. Someone throws a brick through Susan and Jon’s bedroom window, narrowly missing Bella’s crib. Susan is doxxed online and receives death threats. Then, a startling discovery emerges: A woman named Savannah Holmes has been murdered at 26 Oakpark in Loughlinstown, the same street number and name as Susan’s address in a different part of the suburb. The bodies of a married couple have also been found in nearby Cherrywood. Susan has never met Savannah but has been receiving her misdelivered packages for years. They share similar builds and dark hair, and Susan followed Savannah’s social-media posts, envying her glamorous lifestyle. Susan’s sister Leesa, who lives nearby with her husband and their daughters, 17-year-old Maeve and 13-year-old Aoife, theorizes that someone targeting Susan went to the wrong house and killed Savannah by mistake.

Susan and Leesa visit Bar Four and learn that the married couple found murdered in Cherrywood are Aimee Quinlan, the public-relations (PR) woman referenced in Susan’s message, and Aimee’s husband, Rory. Aimee’s sister, Venetia, works as a bartender at Bar Four.

Meanwhile, Susan discovers that Jon is having an affair. She finds a rose-gold bracelet inscribed with a one-month anniversary message from Jon hidden behind his nightstand. Tracing his credit-card charges, she connects the affair to Savannah through a restaurant receipt noting a tree-nut allergy, the same allergy Savannah had. Susan doesn’t confront Jon, fearing that he could use her postpartum mental-health struggles against her in a custody battle. Jon realizes that Susan knows about his affair and secretly fears that she may have killed Savannah.

Through Venetia’s perspective, the novel reveals the truth behind the Cherrywood murders. On the night when Susan’s message went viral, Venetia was visiting Aimee and learned that her sister was eight weeks pregnant. Venetia persuaded Aimee to leave Rory, who had been abusing Aimee and had caused her to lose a previous pregnancy. Later, Venetia saw Susan’s viral message implying an affair between Aimee and Warren and raced to Aimee’s house with her husband, Felipe. They found Aimee beaten to death; Rory had fallen asleep nearby. In a rage, Venetia bludgeoned Rory to death with a barbell. She then drove to 26 Oakpark to confront Susan but went to the wrong address, barged in, and mistook Savannah for Susan. Venetia shoved her against a wall and threatened to kill her before Felipe dragged her away. Neither realized that this woman was not Susan.

In the following days, Venetia launches a campaign of psychological torment against the real Susan, sending death threats and secretly entering Susan’s house and garden. She pulls Bella into direct sunlight to cause a minor sunburn; grabs the baby’s arm, leaving marks; and moves Susan’s trolley containing Bella at a supermarket. Meanwhile, Susan becomes friendly with Felipe, who confides that his wife is emotionally unstable. Their conversations lead Susan to believe that she made a mistake. The woman she saw Warren with was Venetia, not Aimee.

The novel’s teenage characters also experience fallout from Susan’s WhatsApp message. Celeste’s daughter, Nika, is bullied by classmates after Susan exposed her secret relationship with another girl’s boyfriend. She retaliates by posting pages from Leesa’s daughter Maeve’s stolen childhood diary on an anonymous Snapchat account. The diary contains a confession of a private crush, and Maeve is devastated. Ground almonds appear on a brownie in Nika’s lunchbox at hockey camp, a potentially lethal trigger for her tree-nut allergy. Greta, Susan’s eldest sister and the camp’s coach, confiscates the food. She takes the blame to protect her niece Maeve, whom she suspects is responsible.

Flashback chapters reveal what happened at Savannah’s house the morning she died. Jon visited Savannah after she discovered that he was married and threatened to tell Susan about their affair. Jon panicked and called Greta, persuading her to come to Savannah’s house and impersonate Susan. However, Savannah saw through the deception, realizing that Greta was not Jon’s wife.

Events converge on Thursday evening. Nika, driving her mother’s car and believing that Maeve spiked her lunch, spots Maeve walking home from babysitting, mounts the curb, and hits her. Maeve is knocked unconscious with a head injury. Nika’s brother, Cody, finds Maeve and calls an ambulance. However, a neighbor assumes that he’s the attacker based on his history and reports him to the police. That same night, Susan, who’s been staying with Leesa to avoid Jon, returns home with Greta to collect some belongings. She leaves Greta in the kitchen with Bella. Downstairs, Susan discovers Venetia in the kitchen holding Bella; Greta is crumpled on the floor with a head wound. Venetia forces Susan to make a choice: She must kill Greta with a syringe of heroin, or Venetia will kill Bella. Greta insists that Susan choose her and secretly swallows a handful of naltrexone, a medication she takes for long COVID that also blocks the effects of opioids. Susan injects Greta, who collapses.

Venetia flees with Bella in her car. Felipe, who has tracked Venetia, deliberately crashes his car into hers. When Venetia pulls Bella from the wreckage and raises a knife, Felipe throws himself over the baby, taking the blade in his back. Susan strikes Venetia unconscious with a tire iron, and Bella survives, shielded by Felipe’s body. Felipe dies in Susan’s arms.

Greta survives because the naltrexone counteracts the heroin. The official inquest concludes that Savannah’s death was accidental: She slipped on spilled rum in her hallway and hit her head on a radiator. However, the truth is disclosed through Greta’s narration. Greta had long suspected that Savannah caused the car accident years earlier that left her with a permanent limp. Savannah’s then-husband had covered for his wife, who was driving drunk. After Greta unsuccessfully posed as Susan and Jon left Savannah’s house that morning, Greta confronted Savannah about the accident. When Savannah confirmed the truth with smug indifference, Greta pushed her hard. Savannah fell, hit her head on the radiator, and died. Greta staged the scene by spilling rum to suggest a slip and altering evidence on Savannah’s phone to misdirect investigators. No one else knew the truth.

One year later, Susan and Jon have separated amicably. Celeste and Susan have become friends, bonded by their children’s suffering. Nika awaits sentencing, while Maeve has recovered from the hit-and-run. Susan continues therapy, haunted most by Felipe’s death. The narrative reveals that Aoife spiked Nika’s brownies, but her secret remains safe.

On the eve of the next Oakpark summer party, neighbor Juliette Sullivan sends an insensitive joke about last year’s events. Susan takes a screenshot and begins an angry reply to her sisters, but she then stops and deletes everything. After putting down her phone, she kisses Bella and picks up her book.