Someone We Know is a 2019 mystery thriller by Shari Lapena, a Canadian author best known for her 2016 bestseller The Couple Next Door. A terse whodunnit with plot twists and satirical humor, Someone We Know probes the complacency and paranoia of its suburban setting, where everyone has secrets and no one quite knows their neighbors. A New York Times bestseller, Someone We Know uses its murder-mystery plot to explore themes of trust, deception, parenthood, alienation, and the ambiguous boons of modern technology.

This guide refers to the 2019 Penguin Books paperback edition of Someone We Know.

Content Warning: The source text contains a graphic description of murder, as well as instances of substance use disorder and sexuality.

Plot Summary

In first-person point of view, the brutal murder of a young woman is graphically described by her unidentified killer, who kills her with a hammer. The text then shifts to third-person omniscient narration, and three days later, in the idyllic Hudson Valley town of Aylesford, a twenty-something lawyer named Robert Pierce reports his wife Amanda missing to the police. Twelve days later, an Aylesford suburban mother named Olivia sees text messages on her son’s cell phone suggesting that he breaks into neighbors’ houses at night. When she confronts 16-year-old Raleigh, he claims to have only broken into two houses, but he has actually broken into many more. He also lies about where he was the previous night, which is not revealed to the reader. He tells his mother he was hacking into the homeowners’ computers, just for “fun” and sent some prank emails from one of their accounts. Olivia forces her son to show her the two houses he broke into, and eventually delivers anonymous letters of apology to both of them. One of the houses is Robert Pierce’s; the other house belongs to Carmine Torres, a middle-aged widow who has just recently moved to Aylesford. The letter of apology alarms Carmine, and she resolves to find out who wrote it.

Two detectives, Webb and Moen, investigate a car that has been found submerged in a lake in the Catskills, about two hours from Aylesford. A search of the trunk reveals the bludgeoned body of a young woman. Robert Pierce identifies the body of his wife and lies to the detectives when he says that they had a happy marriage. After they leave, he buries his wife’s secret second phone in his garden.

At a book club meeting, Olivia and other women from the neighborhood discuss Amanda, recalling a yard party in which Amanda flirted with all of the men while her husband looked on passively. Robert, alone in his house, recalls drugging his wife shortly before her disappearance so he could find the burner phone she used to conduct her extramarital affairs. Detectives Webb and Moen find out that Becky Harris, Robert’s next-door neighbor, is having an affair with him; she insists that Robert is harmless. Meanwhile, Carmine Torres knocks on Olivia’s door and shows her the anonymous letter. Olivia reacts guiltily, making Carmine suspicious. To calm herself, Olivia talks to Glenda Newell, her neighbor and best friend, who also has a troubled 16-year-old son, Adam, who has a substance use disorder with alcohol.

Meanwhile, Becky Harris shares that shortly before Amanda’s disappearance, she saw her arguing in a car with Olivia’s husband, Paul; she believes that they were having an affair. The detectives question Paul, who admits to meeting with her in her car, but says he was merely warning her to stay away from Larry Harris, Becky Harris’s husband, after catching them in an act of oral sex at work. The detectives question Larry and Becky about this, and Larry admits the sex but denies that he was in a relationship with Amanda. He insists that he was at a conference in the Catskills at the time of her murder, but the police cannot corroborate this. Paul, too, has a very weak alibi, and Robert Pierce has no alibi.

Carmine, sleepless from her anxiety over the break-in, hears noises one night and sees a drunken teenager staggering past her driveway, brandishing a broken hockey stick. She later recognizes him as Adam Newell, Glenda’s son.

The police acquire surveillance footage of Larry Harris visiting a hotel with Amanda Pierce, proving a long-term affair. They also learn that Paul Sharpe owns a small cabin near the lake where Amanda’s body was found. He agrees to let them search it, and they discover a hammer missing from the toolbox in the cabin’s shed. A forensics team uses luminol to detect blood on the kitchen floor, walls, and ceiling. Consequently, they arrest Paul Sharpe for the murder of Amanda Pierce. Paul’s lawyer, however, argues that the evidence against him is largely circumstantial. Meanwhile, Glenda Newell is baffled when Carmine Torres knocks on her front door and claims to recognize her son Adam from something unspecified on a previous night.

The police release Paul Sharpe, hoping that it will shake up the other suspects and lead to a break in the case. When Paul returns home, his son Raleigh tells him that a week or so earlier, he broke into Keith and Glenda Newell’s house and found emails on their computer suggesting an affair between Keith and an unknown woman. Since the Newells frequently vacationed at the Sharpes’ cabin, Paul decides to tell the police about Raleigh’s discovery. The police search Keith’s computer and find the emails, and Keith confesses to an affair with Amanda. He says he had a liaison with her at the Sharpes’ cabin the Friday she disappeared: He left her there on Friday evening and returned the next day to find her gone. However, the police catch him in a lie concerning the cabin’s spare key.

The detectives learn that Carmine Torres has been strangled to death in her home. Zoe, her next-door neighbor, reports seeing Glenda Newell at Carmine’s front door late that night. Glenda confesses to the murders of both Carmine and Amanda, but the detectives still believe that Amanda was murdered by someone else. The narrative shifts back to the first-person point of view of the killer—Adam, Glenda’s teenage son. He says that weeks earlier, he found his father’s emails to Amanda on the computer and went to the cabin to confront his father’s lover. He then killed her with a hammer. In a panic, he called his mother, who quickly decided to cover up her son’s crime. The point of view returns to third person, as the detectives tell Glenda that her son will probably only serve a couple of years. She, however, will go to prison for much longer for the murder of Carmine, whom she killed because she thought she might have seen her and Adam driving home in separate cars after disposing of Amanda’s body.

Robert Pierce, delighted at the way things have turned out, sneaks out to his garden to dig up his late wife’s burner phone, which contains unspecified evidence against him. However, it is missing, and he suspects that Becky Harris has stolen it. In a cold rage, he stares at her house, plotting what to do next.