The novel opens with a series of anonymous text messages sent to a woman named Dani, escalating from friendly overtures to explicit surveillance of her apartment, her cat, and her body, and culminating in the threat: "Make a list of everything that terrifies you. That's me" (x).
A prologue set three years before the main action introduces Dr. Sara Linton, a pediatrician working the overnight shift at Grady Memorial Hospital in Atlanta. Nineteen-year-old Dani Cooper arrives after a low-speed car crash, but her injuries, including a collapsed lung and a flail chest (multiple broken ribs causing part of the chest wall to move independently), are far too severe for a minor collision. Before losing consciousness, Dani whispers that she was drugged and raped, begging Sara to stop the man who hurt her. Despite Sara's desperate attempt to manually pump Dani's heart through an abdominal incision, Dani dies. Sara silently promises to stop the man responsible.
Three years later, Sara testifies in a civil wrongful death trial brought by Dani's parents against Tommy McAllister, the 22-year-old son of prominent cardiologist Mac McAllister and his wife Britt. Sara tells the jury that Dani's injuries indicate a brutal beating, not a car accident, and that Dani disclosed being drugged and raped. Defense attorney Douglas Fanning cross-examines Sara aggressively but drops a planned attack on her personal history, including the fact that Sara was raped 15 years earlier by a hospital janitor named Jack Allen Wright.
After testifying, Sara retreats to the courthouse bathroom, where Britt bursts in, sobbing and sedated. Britt admits she knows Tommy raped Dani and that "Mac is always involved" (42). She tells Sara that Sara's assault and Dani's death are "all connected" (42), asking, "Don't you remember the mixer?" (42). The mixer was a monthly Friday gathering of medical residents at a bar near Grady. Before Sara can press further, Britt regains her composure and storms out.
That evening, Sara confides in Faith Mitchell, the partner of her fiancé, Special Agent Will Trent of the Georgia Bureau of Investigation (GBI). For the first time, Sara reveals the full scope of her assault: Wright drugged her, handcuffed her, stabbed her, and raped her. The resulting ectopic pregnancy led to emergency surgery and a hysterectomy. Sara lays out the parallels between her attack and Dani's: both were preceded by threatening messages, both involved drugging, and both women were wounded on their left sides. Faith notes how common such attacks are but concedes the pattern when Sara adds that Britt explicitly declared the connection is real.
Sara, Will, and Faith begin an unofficial investigation, mapping the members of a social group they call "the gang": medical residents who attended the monthly mixer, including Mason James (Sara's boyfriend at the time), Sloan Bauer, Cam Carmichael, Chaz Penley, Richie Dougal, and others. To infiltrate Britt's social circle, Will contacts his estranged aunt Eliza, a dying widow and longtime member of the Piedmont Hills Town and Country Club. Assuming the alias John Trethewey, Will encounters Mac and Richie at the club bar. Sara separately confronts Britt in the club's steam room, where Britt drops the name Merit Barrowe, a 20-year-old patient who came into Grady drugged and claiming rape, then died of a seizure two weeks before the mixer.
Will and Faith meet Martin Barrowe, Merit's brother, a defense attorney who as a teenager investigated his sister's death. Martin reveals that Detective Eugene Edgerton dismissed the case despite evidence of assault, fabricating a narrative of accidental overdose. Cam Carmichael, Merit's attending doctor, had written "Suspicious. Non-accidental overdose. Sexual assault" (169) on her original death certificate, but Edgerton forced him to complete a falsified replacement. Edgerton approached Cam one day after Sara's rape, suggesting he deliberately prevented investigators from connecting the two assaults. Martin provides Cam's old laptop, containing password-protected files and a chat website with seven anonymous members.
Meanwhile, college student Leighann Park is injected with a drug at a pop-up dance club and surfaces 36 hours later with no memory, missing underwear and a left shoe, bruises, and the words "That's me" written in permanent marker on her body, echoing the anonymous texts sent to Dani. All three victims, Merit, Dani, and Leighann, were missing their left shoes.
Sara flies to New York to confront Sloan Bauer, who reveals that Cam raped her on their first date in medical school. Before his suicide, Cam mailed Sloan Merit's underwear from the night Merit died. Sloan kept the evidence for eight years and turns it over to Sara. Faith's son Jeremy cracks Merit's old iPhone, restoring deleted chat transcripts that reveal the gang's panic after Cam's suicide. Separately, Faith reads decrypted files from Cam's laptop describing the gang's secret conspiracy, which they call "the Club": Members rotate roles, with one stalking the victim, another sending threatening texts, another abducting, another drugging, and a designated "Master" committing the rape.
Sara makes the critical discovery linking the victims: Merit, Dani, and Leighann all had childhood heart conditions repaired by Dr. Nygaard's surgical team at Grady, with Mac as the fellow or resident who performed follow-up care. Mac selected victims from among his former pediatric cardiac patients, identifiable by their surgical scars.
Sara, Will, and Faith present the case to Deputy Chief Amanda Wagner, who authorizes an undercover operation and recognizes the potential for a RICO (Racketeer Influenced and Corrupt Organizations) prosecution. Jeremy, wearing glasses with a hidden camera, poses as Will's son "Eddie" at the gang's Friday mixer. Will records Mac offering a million-dollar bribe for silence about the Club. Outside the bar, Chuck Penley, Chaz's son and Tommy McAllister's friend, shows Jeremy a phone video of Dani being raped on a white sheepskin rug, casually noting Tommy sent it.
Sara, wearing a wire, confronts Britt at the McAllister mansion. Recognizing Britt's verbal patterns from the chat transcripts, Sara identifies Britt as poster 002, the organizer who ran the Club from her own home. Britt attacks Sara with a tennis racket, breaking her wrist and nose. When the transmitter falls from Sara's jacket, Britt makes a calculated confession into the camera: She claims responsibility for beating Dani, organizing the Club, filming the rapes, and storing videos on a basement server. She displays nearly 50 left shoes taken from victims.
Britt then reveals that she orchestrated Sara's rape 15 years ago by manipulating Wright, leaving handcuffs in his locker, putting an emetic in Sara's drink to make her sick, and funneling her to the right bathroom, all to prevent Sara from accepting a prestigious fellowship so Mac could receive it instead. Britt picks up a revolver that fell from Sara's purse, presses it to her head, and declares a dying confession. Sara mutes the microphone and tells Britt how to cock the hammer. Britt shoots herself.
In the aftermath, Mac and Tommy take plea deals and will likely die in prison. Chaz Penley receives 20 years; Richie Dougal receives 10. Mason James faces no charges. Sara tells Will that knowing Britt orchestrated her assault has paradoxically relieved some of her 15-year guilt. Will takes Sara's engagement ring, which features a green glass stone and belonged to his mother, to a jeweler to repair a scratch. In the final exchange, Will asks if their marriage will be forever. Sara answers, "I do" (421).