The Chestnut Man

In 1989, police officer Marius Larsen drives to a remote farm on the Danish island of Møn. Inside, he finds the farmer Ørum's two teenage children shot dead and Ørum's wife hacked to death with an axe. In the bathroom, Larsen discovers a young boy barely alive beneath a shower curtain. Remembering the boy has a twin sister, he descends to the basement and finds the girl cowering in a room used as a prison. An adjoining room holds hundreds of handmade chestnut dolls. The boy appears behind Larsen and kills him with the axe.

The novel shifts to present-day Copenhagen, where dental nurse Laura Kjær is found murdered in a playground behind her home, her right hand amputated. Naia Thulin, a young detective in the Major Crimes Division, is assigned the case alongside Mark Hess, a disengaged liaison officer sent home from Europol after a disciplinary dispute. Thulin is a single mother eager to transfer to NC3, the National Cyber Crime Center, while Hess wants only to return to Europe.

That same day, Rosa Hartung, the minister for social affairs, returns to parliament. Her daughter, Kristine, disappeared nearly a year earlier, and a young man named Linus Bekker confessed to killing and dismembering her, though the body was never recovered.

A small doll made of chestnuts is found near Laura Kjær's body. Simon Genz, the head of the Forensics Department, reveals that a fingerprint on the doll matches the prints of the presumed-dead Kristine Hartung. Rosa recalls that Kristine made and sold chestnut dolls, seemingly explaining the fingerprint. Nylander, Thulin's boss at Major Crimes, accepts this explanation, but Hess does not. He visits Laura's son, Magnus, at the hospital, and the boy confirms the doll was not at the playground the day before the murder.

Hess privately examines the Kristine Hartung case and discovers that the machete from Bekker's garage contained blood but no bone dust, casting doubt on its use for dismemberment. Meanwhile, a text message to Laura Kjær's phone leads the detectives to a package containing her amputated hand, addressed to wealthy investor Erik Sejer-Lassen. Thulin realizes the killer's target is Sejer-Lassen's wife, Anne. They race to the home but arrive too late. Anne's body is found in a nearby forest, both hands amputated, with another chestnut man bearing Kristine Hartung's fingerprint.

Hess argues the killer is constructing a human chestnut man, amputating limbs to mirror the doll's form, and urges Nylander to reopen the Hartung case. Nylander refuses. The detectives uncover a pattern: Both mothers were anonymously reported to a whistle-blower scheme Rosa championed, accused of failing to protect their children. In both cases, the children were in fact being abused: Laura's boyfriend had been sexually assaulting Magnus, while Erik Sejer-Lassen had been abusing his daughters.

Hess reasons the killer has already filed a third report identifying the next victim. Sifting through tips, they identify Jessie Kvium, a single mother at the Urbanplan housing estate. Thulin impersonates Jessie in an undercover operation, but the killer outwits the police and strikes where Jessie has been placed under guard, killing her. Jessie's daughter survives unharmed.

As the media leaks information about Kristine's fingerprints, detective Tim Jansen, who helped secure Bekker's confession, uncovers two suspects: Benedikte Skans, a nurse, and her boyfriend, Asger Neergaard, an ex-soldier. Their child was removed under Rosa's policies and later died. Jansen raids their residence, finding surveillance material targeting Rosa, and discovers that Neergaard has been serving as her ministerial driver. Before Neergaard can be arrested, he kidnaps Rosa's son, Gustav.

A massive search ensues. Genz murders the couple, then contacts Nylander, claiming to have tracked them via GPS. The task force finds their bodies in a forest and rescues Gustav unharmed. At the couple's residence, Thulin discovers the amputated remains of the three victims. Nylander declares the case closed. Hess protests, arguing the couple lacked motive and had alibis, but Nylander dismisses him.

Hess is reassigned to Europol, while Thulin accepts the NC3 position. On her last day, a school lesson about chestnuts triggers a realization: The dolls from the crime scenes were made from a rare edible chestnut hybrid, not the common horse chestnuts in the Hartung garden. Thulin seeks Genz, believing him an ally, and he drives her to Møn. They find the rare trees near a road leading to the renovated Ørum farmhouse, the site of the 1989 massacre. Inside, Thulin discovers an evidence wall with photos of the victims. Genz reveals himself as the killer, strikes her, and locks her in his car's trunk.

At Copenhagen Airport, Hess opens a delayed email containing crime-scene photographs that Bekker frequently viewed. Among them is a photo from the 1989 massacre showing the dead policeman and, behind him, shelves of chestnut dolls. Hess realizes the chestnut man is a serial killer's signature spanning decades. He forces his way off the plane and interviews a retired inspector, who describes how the Ørum family abused the foster twins, forcing the boy to make chestnut dolls. From a class photo, Hess recognizes the boy as Genz. Tracing the twins' history, he discovers they once lived with the Petersens, whose adopted daughter was Rosa Petersen, now Rosa Hartung.

A flashback to 1987 reveals the pivotal event. Young Rosa taught the foster twins to make chestnut men, and her parents planned to adopt them. But Rosa, struggling with jealousy, fabricated a story that caused social workers to remove the children. The twins were sent to the Ørum farm, where years of abuse followed. As they were driven away, they left Rosa five chestnut dolls arranged in a family circle, holding hands.

In the present, Rosa finds an identical arrangement of chestnut dolls on her doorstep. She and her secretary Liu search old foster-care records and locate the farm's address. Rosa drives to Møn alone. Genz drugs her, straps her to an operating table, and begins amputating her hands while narrating how he kidnapped Kristine and moved her to an undisclosed location.

Hess races to the farm but is ambushed by Genz in the basement. Bound and doused in gasoline as Genz sets the room ablaze, Hess cuts his bonds, frees Rosa, and breaks through a basement window. He drags her into the snow, then intercepts Genz's fleeing car. Thulin, still locked in the trunk, breaks through the backseat and attacks Genz, causing the car to crash. Genz is impaled on a chestnut branch and dies without revealing Kristine's location.

Investigators trace Genz's GPS history to an area near Rostock, Germany, and find a rental car registered to his twin sister, Astrid Bering. German police locate Astrid at a cottage near the Polish border, where she has been keeping Kristine for over a year. The Hartung family travels to Germany, and when the task force surrounds the cottage, Kristine emerges and runs toward her parents. The family is reunited.

In the aftermath, Hess visits his late wife's grave for the first time and buries his wedding ring beneath the gravestone. At the airport, Thulin does not come to say goodbye, but she sends him a photo of Le's school family-tree poster, onto which her daughter has added Hess's picture. Hess laughs as he boards his flight. In a chilling final scene, Bekker, released from custody, sits on a train and smiles at a single mother and her young daughter.