You Know Why

The novel opens with two prologue-style chapters. The first presents a fragmented Christmas Eve scene: a pregnant young woman found dead near bloodied scissors in her decorated cottage. Her husband was on a plane at the time of death. A grand jury declines to charge him, and he disappears. A narrator introduces herself as Eden and declares that her younger sister Chloe was murdered 11 years ago, that the killer walked free, and that she intends to make things right.

The main narrative begins in Franklin, Tennessee. Brooklyn Locke, a former travel food photographer, lives with her husband Trey and their children, nine-year-old Four and seven-year-old Neve. Trey surprises Brooklyn with a last-minute trip to Italy, claiming his boss and uncle-by-marriage, Bob Gussin of the venture capital firm the Gussin Group (TGG), needs him at a conference in Milan. Brooklyn is suspicious because Trey hates to fly but scrambles to prepare. Her twin sister, Margot, stays behind. That night, Brooklyn receives a threatening email demanding money, which vanishes from her inbox moments later.

At the Nashville airport, the family is rerouted through Atlanta. Trey reacts with alarming fury. On the connecting flight, a woman named Eden Barrow approaches Trey, calling him "Andrew" and mentioning her sister Chloe. Trey denies knowing her. At Hartsfield-Jackson Airport in Atlanta, Trey excuses himself before the overnight flight, kisses Brooklyn, and promises to explain everything later. He never returns. Security footage shows him leaving the terminal in a black SUV. His phone is found in a trash can with its passcode changed. Eden reappears, claiming to work for the airline, and offers to help with the children.

Eden's perspective reveals her as Chloe's older sister. She recognizes Trey as Andrew Locke, the man she believes murdered Chloe. She has spent 11 years searching for him and resolves to use Brooklyn's trust to get close to the family, privately fixated on claiming the children as her own.

Brooklyn's crisis deepens. Uncle Bob denies knowing about any trip, and her bank reveals Trey has emptied their accounts. Unable to afford a hotel, Brooklyn accepts Eden's offer to stay at her home. There, Eden's friend Detective Theresa Lee of the Malogen, Georgia, Police Department confirms that Brooklyn's husband is Andrew Locke, a former Air Force pilot, not from Connecticut as he claimed. Eden reveals that Trey was married to Chloe and was the primary suspect in her murder. Brooklyn experiences a severe panic attack and runs into the street, where a waiting SUV strikes her, causing a severe concussion.

A chapter from Trey's perspective reveals that a blond man ambushed him in the airport bathroom, threatening his family. The man, later identified as Aleksey Durov, a Russian national wanted by Interpol, forced Trey into the SUV and demanded money, implying involvement in Chloe's murder. Trey fights free and later visits Brooklyn at the hospital, insisting he did not do what they accused him of.

Detective Lee contacts FBI Agent Drake Sheehan at Quantico, who confirms Andrew's identity and reveals that the Gussins reported him for embezzling tens of millions from TGG. That night, an intruder attacks Theresa in her home, demanding Andrew's whereabouts. The next morning, she discovers Andrew's parents murdered at their estate.

At the hospital, a second attempt is made on Brooklyn's life: security cameras go offline, a man in scrubs enters her room, and she goes into cardiac arrest. Doctors find nicotine in her bloodwork, indicating poisoning. Margot arranges Brooklyn's transfer to Vanderbilt in Nashville. Eden moves into the Locke household, growing possessively attached to the children.

Brooklyn wakes with severe memory deficits and associative prosopagnosia, a form of face blindness. She gradually reconstructs her life through conversations with Margot. FBI agents show her video of the SUV that struck her and assert the driver was Trey, telling her he is suspected of attempted murder and embezzlement.

After discharge, Brooklyn finds Eden entrenched: the house reorganized, family photos removed, the children calling Eden "Auntie." A neighbor mentions seeing Eden at the school weeks before the trip, contradicting her account. Brooklyn demands Eden leave. In the storm shelter behind the house, Four reveals what Trey hid: crypto wallets and a burner phone. Brooklyn contacts Trey, who confirms he is alive and begs her to remember what he told her in Argentina.

Brooklyn's memory returns. In Bariloche, Argentina, near the end of her first pregnancy, Trey confessed he worked for a government agency and had been sent to find her. The French government suspected her of involvement in Roger Bandolier's overdose death during a photography shoot in Thiviers, France. Trey paid off those tracking her and quit his position, vowing to protect her.

At the FBI's Nashville office, a database search triggers a classified file. Special Agent in Charge John Baldwin reveals that Andrew has been a confidential informant for a decade, embedded in TGG through Operation Angelmaker, a covert task force targeting the firm's cartel money-laundering operations. Trey explains that the Gussins' organization sabotaged his Air Force plane and killed Chloe to pressure his father into surrendering classified weapons data. Trey fell in love with Brooklyn while undercover. The money he appeared to steal was part of the operation; Bob Gussin blamed Trey to cover his own theft from the cartels.

Flashbacks reveal that during Chloe's adolescence, she experienced mysterious chronic illness that vanished whenever she was away from Eden. A hospital identified nicotine poisoning: Eden had been lacing Chloe's food with liquid nicotine, a pattern consistent with Munchausen syndrome by proxy, in which a caregiver deliberately makes someone in their care sick. Confronted by her parents, Eden checked herself into a psychiatric facility rather than face arrest. Chloe obtained a restraining order.

Eden poisons the Locke household's food with liquid nicotine, incapacitating the children, Margot, and FBI agents. She drinks a dose herself and blames Brooklyn. Trey identifies the poison based on Eden's history, enabling treatment that saves the children.

Detective Lee presses Brooklyn about Bandolier's death. Brooklyn reveals that Durov, who went by Alex, was her boyfriend and the crew's drug supplier in Thiviers. During a riverside outing, Alex and Roger fought; Brooklyn grabbed a gun and accidentally shot Alex. Roger told her Alex was dead. That night, with Margot posing as Brooklyn to provide an alibi, Roger consumed fentanyl-laced cocaine from Alex's bag and died.

Durov arrives at the house, shoots Detective Lee (whose bulletproof vest saves her), and forces Brooklyn into the underground shelter at gunpoint. He reveals the Gussins hired him and that Eden rerouted the family's flights through her airline access. He shoots Brooklyn in the leg. Trey arrives, battered and limping, and throws a crypto wallet to buy time. Durov shoots out the lights, and in the darkness, Drake fires a single shot that kills him. Brooklyn sustains a second wound but survives.

The Gussins are arrested and charged with conspiracy, money laundering, and racketeering under the Racketeer Influenced and Corrupt Organizations (RICO) Act. Eden lies in a coma from her self-administered nicotine overdose. The family relocates to Venice, Italy. In a private farewell, Brooklyn thanks Margot for keeping silent, confirming both sisters conspired in the deaths in Thiviers. In a final chapter, Eden's coma monologue reveals the novel's deepest secret: On Christmas Eve, she went to Chloe's house to talk, but Chloe announced her pregnancy and ordered Eden to leave. Chloe tripped and fell onto the scissors. Eden cleaned up, returned as Andrew found the body, and screamed to frame him. The novel ends with doctors noting increased brain activity in Eden, suggesting she may wake up.