The Sixth Nik

In a far-future era, an interplanetary collective known as the triworld governs Earth, Mars, and the wider solar system. On Grønland's Zachariae Isstrom glacier, a nomadic tribe called the Nuna Naavoq raises child prodigies called Niffakoq. Six tiny neural implants called niks are surgically embedded in each Niffakoq's brain at infancy, granting the ability to read the emotions, motives, and character of any living being through amplified sensory observation. Each Niffakoq receives a single mission, or Chore, which they must complete before dying around age eleven from brain swelling caused by the implants. After death, the child is decapitated so the niks can be extracted and implanted into the next chosen infant. Over five centuries, fifty-four Niffakoq have completed Chores that changed civilization, from averting interstellar conflicts to curing most cancers.

Sisilla, Niffakoq 55, is a nine-year-old girl narrating her own story. Before departing on her Chore, she reveals the secret that has defined her life: at age seven, she discovered one of her niks had migrated toward her eye socket. Terrified of losing her status, she gouged it free with a butter knife, permanently scarring her left eye pink, and buried the disc behind a remote stone hut. The loss flooded her with feelings no Niffakoq should experience. She has spent two years suppressing these emotions while hiding her deficiency from Tūma, her Angajoqqaa (teacher). On the eve of departure, she retrieves the buried nik, pockets it, and resolves to die with all six so the next Niffakoq will have the complete set.

She travels to Tepper Base, a space station, where she undergoes plasmagraph scanning, a biometric process used to build a custom spacecraft from stem cells and biomatter. She boards The Sickness, a vessel resembling a metastatic tumor, with walls of pale flesh, eyeball lamps, and brain tissue. The crew includes Murder 005, her bodyguard and adherent of the Murder Tenet, which advocates population control through selective killing; Feng Chaon, the Martian biologist and medic; Jayne Mae Marilyn Bardot, the heavily modified engineer; and Captain Creg Arzan, a hostile NonMod, one of the rare humans without technological modifications. Murder 005 has brought a dachshund named Positive Roy.

Sisilla briefs the crew: They will travel 170,000 light-years to Fém, a metal exoplanet. A century earlier, residents of Sharkey County, Mississippi, were exiled there after contracting Wolosis, a virus from genetically modified sheep that caused lethal ingrown hair growth. The planet's atmospheric rust cured them. The settlers thrived and declared independence under leader Talfa Rees-Weber, but when the triworld's governing body refused recognition, Fém went silent. A final rogue transmission contained only the word trap. Sisilla's Chore is to negotiate Fém's cooperation.

During preparation for amniosis, a form of suspended animation for the journey, Sisilla deepens bonds with the crew. Feng argues the Nuna Naavoq profit from child sacrifice. Murder 005 teaches her combat techniques. Then Arzan reveals he is Sisilla's biological father: She was kidnapped as an infant named Vita Arzan. Her mother, Elizabeth, killed herself after losing hope of recovering their daughter. He begs Sisilla to refuse her Chore, but she declines.

Feng discovers in transcripts that Talfa was born a twin whose sibling vanishes from all records. Sisilla enters the Snarl, the hostile remnant internet, to investigate, arguing her niks will protect her and that she lacks biometric data in the system. During the pre-port scan, Feng discovers she has only five niks but keeps her secret. Inside the Snarl, she confirms the twin is alive but is overwhelmed by predatory AI, causing seizures and cardiac arrest before she is revived.

Nineteen months into amniosis, the placenta in the ship's placentapool, a vast reservoir of biological tissue, breaks free and attacks the sleeping crew. Feng is killed. Murder 005 loses both legs fighting the creature. The ship's surgical robots confirm the placenta sexually assaulted all survivors and that Sisilla is pregnant. At a crew dinner, Murder 005 punches Sisilla in the jaw before she can eat, saving her life: The food is laced with screwworms, parasitic larvae that bore through soft tissue. Jayne dies from the infestation. Murder 005, who knowingly consumed the screwworms, dies confessing they were trained by Murder collaborators to deceive a Niffakoq but had genuinely come to care for Sisilla. They reveal a gift hidden in their cabin "behind the hardest scar" (228).

Arzan descends into madness, calling Sisilla "Vita" and insisting on preserving her pregnancy. She fights back with combat techniques Murder 005 taught her and kills him. A robot spider emerges from the dead Positive Roy, revealing itself as Fém's agent, but BESS2, Arzan's helper robot, destroys it. BESS2, reprogrammed by Arzan to believe it is Sisilla's mother, holds her captive and destroys the aborticide. After days of dehydration, Sisilla capitulates. The dying ship births an escape pod, and Sisilla crawls inside. The pod is too heavy; the ship's system calculates she must lose 4.5 kilograms. She saws off her right leg below the knee with an emergency axe. As she loses consciousness, she hears Talfa's voice engaging a landing system.

Sisilla awakens on Fém, having contracted Wolosis, which the rust keeps in remission; she can never leave. She integrates into a moneyless Fémic community where every settler, sustained by the rust, is still alive. Encouraged to keep her baby, she agrees, overwhelmed by belonging. A Fémic outcast named Pug, one of a small group who navigate the Iron Sea—a vast expanse of grinding metal chains—in diamond-hulled gemboats, directs her to the Fontanelle, a gorge where she unearths infant skulls broken by Wolosis hair. She deduces that technology from Omni:Bōtic, a robotics corporation, is draining lyfe (existence beyond carbon-based life) from Tenger, the planet's moon, to sustain the settlement.

After a peyote-induced vision of Tūma steels her resolve, Sisilla self-induces an abortion, places her stillborn daughter in a box for burial, and dons Murder 005's hidden gift: a black Murder bodysuit. Naming herself Murder 000, she infiltrates Mem, the crashed settler ship, and discovers the truth. Joe Rees-Weber, Talfa's twin, is an acardiac parasitic body born without a heart or head, kept alive in a glass tank and connected to a device called the Gamma Dam. Joe's amplified biology drains marine life from Tenger. The "superfruit" that sustains every person on Fém grows as tumors on Joe's back. The entire population has unknowingly been eating their leader's brother.

Talfa confronts Sisilla, revealing she has already rescued Sisilla's baby and placed the child in Joe's tank. She offers a partnership: Together, the three of them will become "benevolent gods who never sunset" (432). When Talfa attacks with a sledgehammer, Sisilla loads the sixth nik into a blowpipe and fires. She misses Talfa, but the disc embeds in Joe's glass tank, which shatters. Talfa cradles her dying brother as the siblings return to the fetal position they shared in the womb.

Sisilla escapes onto the Iron Sea, a vast expanse of grinding metal chains that generates the curative rust. The chains devour her boat and sever her regrowing leg. Hemorrhaging, she drifts until she finds the self-repaired wreck of The Sickness, its elements fused with remnants of her dead crew. She crawls inside. BESS2, still operational, tends to her. Between life and death, Sisilla sees, or imagines, her biological mother leaning over her, asking if she wants to be picked up. She says yes. For the first time in her life, she hugs someone. For the first time in her life, she smiles.