It's One of Us

The novel opens with a lyrical prologue describing a woman's body submerged in a lake, slowly becoming part of the aquatic ecosystem while her family searches in vain. The police eventually recover the body, and the central question emerges: Will they find the killer before he strikes again?

Olivia Bender, a successful Nashville interior designer, discovers she has miscarried for the sixth time. She and her husband, Park Bender, a former English professor who now ghostwrites psychological thrillers under a strict NDA, have spent years and enormous sums on fertility treatments. Before Olivia can share the news, Detectives William Osley and Josephine Moore arrive at their door. They inform the couple that DNA found in murdered Beverly Cooke's car has been traced paternally to Park. Their suspect is his biological son.

Park insists he has no children. In the confusion, he blurts out that Olivia is pregnant, violating their agreement to keep the pregnancy secret. Privately, Olivia tells him she lost the baby that morning. After the detectives leave, Park retreats to his backyard office and opens a file from Winterborn Life Sciences, a sperm bank in Chapel Hill, North Carolina, where he donated during graduate school. He never told Olivia about the donation.

A flashback to prom night in 1999 reveals the tangled romantic history at the novel's core. Park and Olivia were high school sweethearts, but when his fraternal twin, Perry Bender, was unexpectedly crowned Prom King, Park stormed off and was caught with another girl. In a rage, Olivia lost her virginity to Perry. Nine weeks later, Park and Perry's younger sister Lindsey, who is also Olivia's best friend, drove Olivia to a clinic in Knoxville for a surgical abortion. Olivia never told Perry about the pregnancy, and the guilt shaped the rest of her life; she privately believed this decision was the reason she could not carry a pregnancy to term.

Meanwhile, 16-year-old Scarlett Flynn is introduced as one of Park's donor-conceived children. She lives with her mother, Darby Flynn, a night-shift oncology nurse, and her older brother Peyton. Using a consumer DNA kit, Scarlett discovered dozens of half-sibling matches and created a private Discord server called "the Halves." A message from another member alerts the group: DNA matching their shared donor has been found at Beverly Cooke's crime scene. The killer is one of them. Darby discovers the group, and Scarlett persuades her to call the police tip line.

The detectives return with staggering news: Park has 28 biological children, 19 of them male, all potential suspects. A flashback recounts Park's time at UNC Chapel Hill, where his girlfriend Melanie Rich went missing and was later found dead in a lake. Park's roommate Peter Johnson was convicted of Melanie's murder and died in prison. Now Moore reveals Melanie was pregnant when she died, and the police plan to exhume her body for paternity testing.

The investigation accelerates when Park's office is broken into and his safe emptied of cash, a gun, his passport, Winterborn files, and thumb drives containing unpublished manuscripts. Olivia encounters the intruder at a job site: a young man with flat, empty eyes who calls himself Griffin White but is later identified as Peyton operating under an alias. He leaves behind Park's stolen documents, including photographs of Melanie Rich. Moore connects the break-ins and warns that another donor mother, Jillian Kemp, has gone missing.

Perry, a nature photographer for the BBC who has been living abroad for years, arrives in Nashville. He is still in love with Olivia. Lindsey persuades him to stay out of the crisis, but Perry unknowingly helps Peyton tie down a ladder near her house. Park's crisis management lawyer, Lucía Perez, arranges a live interview with reporter Erica Pearl to control the narrative. The interview turns disastrous when Pearl ambushes Park with questions about Annie Cottrell, a girl who disappeared from his childhood neighborhood in St. Louis, and a drowning during his college spring break. Olivia steps in defiantly, revealing that someone has been breaking into their home. Afterward, Park drunkenly accuses Perry of leaking information, and Perry punches him.

Darby and Scarlett see the suspect's sketch on the news and recognize Peyton. Darby recalls his troubled childhood: violent tantrums, multiple misdiagnoses, and a terrifying moment at age nine when she found him holding a knife over Scarlett in the bathtub. She committed him to a hospital, where doctors determined that psychotropic medications were inducing schizoaffective disorder. Weaned off the drugs, Peyton returned home at 13, seemingly stable. Now Darby and Scarlett learn he dropped out of college months ago and has been lying to them.

A chapter from Peyton's perspective reveals his obsessive planning. He killed a Winterborn employee to obtain Park's identity, then followed Park and Olivia to a fertility clinic, where he became fixated on Olivia. He has been living in an abandoned barn, holding Jillian captive, drugging her with sedatives stolen from Darby's emergency medical kit, and talking to her about Olivia for hours. Jillian breaks free, strikes Peyton with a chisel, and escapes. State troopers find her alive near Waverly, Tennessee, weeks later. Peyton's DNA matches three additional unsolved homicides.

Olivia, shattered by the discovery that Park has known about at least one donor child for three years, a boy named Brandon to whom he secretly sent gifts, destroys Park's office and flees to a client's beach house in Alys Beach, Florida. There she renovates, heals, and decides to end her fertility journey permanently. Perry finds her and tells her Annie Cottrell's remains have been discovered near their childhood baseball field after an anonymous tip. A witness saw Park near the burial site recently, and Perry suspects Park is responsible for Annie Cottrell's and Melanie Rich's deaths. Their mutual attraction overwhelms them, and they spend the night together. They summon Park to the beach house.

Under Perry's questioning, Park confesses: At age 10, he stumbled on Annie Cottrell's decomposing body and, terrified the neighborhood would blame him, buried her in an old well. He recently called Crime Stoppers anonymously to give her parents closure. He denies killing Melanie Rich.

Peyton appears from the boardwalk, bandaged and wounded, holding a gun. He waves Olivia's stolen letter and says he knows her secret. Olivia activates the emergency signal on her Apple Watch. Park and Perry rush Peyton. In the struggle, Peyton shoots Perry in the arm. Park wrests the gun away and shoots Peyton in the neck. Peyton's dying words are for Olivia: "Don't worry. I'm the only one who knows. I'll never tell" (359).

A final flashback reveals the secret. Years earlier, young Olivia drove to Chapel Hill to win Park back. She overheard a violent argument in his apartment: Park called Melanie a whore and said the baby was not his. Olivia heard a scream, gurgling, and banging before Park snarled at Melanie to get out. Melanie stormed out with bruises on her neck. Olivia followed her to a lake, confronted her, and struck her when Melanie swung first. Melanie fell, hit her head on a rock, and died. Olivia panicked, filled Melanie's clothes with rocks, and pushed the body into the water. She later wrote an unsent letter to Melanie's mother pleading for forgiveness. This is the letter Peyton stole, read, and died clutching. His blood has destroyed it.

In the epilogue, Park and Olivia divorce, bound by the shared secret of Melanie's death. Park marries Darby, and together they raise Scarlett and connect with Park's biological children, now numbering 32. Lindsey marries Lucía. Perry returns to the BBC and never answers Olivia's calls. Olivia lives in Monterey, California, behind gates and cameras, with a five-year-old son named West. He is Perry's child, with his father's soft gray eyes and Olivia's dark hair. She has never told Perry.