The sixth installment in the Grant County series opens with a harrowing prologue: A drugged, unnamed woman sits in the backseat of a car on a high school football field, unable to move as a masked man pours lighter fluid over her. Lena Adams, a Grant County, Georgia, detective, drives the car and begs the man to stop, but he drops a lit lighter onto the victim's lap and her body erupts in flames.
The narrative shifts to Monday afternoon. Dr. Sara Linton, a pediatrician and part-time county coroner in Grant County, endures a brutal malpractice deposition. The parents of Jimmy Powell, a 12-year-old who died of leukemia, are suing Sara for delaying two days before sharing his lab results. Their attorney dredges up Sara's past, including a rape during her medical residency, to argue her judgment was compromised. Sara admits she felt guilty about Jimmy's death. She has closed her children's clinic after over 100 parents signed releases hoping to profit from the lawsuit, and the town has turned against her.
That evening, Sara's husband, Jeffrey Tolliver, the Grant County police chief, brings troubling news: Lena Adams, a detective on his force, has been involved in an explosion in Elawah County and arrested. Sara accompanies Jeffrey on the three-hour drive to Reese, Elawah's county seat, where Lena grew up and where her uncle Hank Norton raised Lena and her twin sister Sibyl after their parents died.
A flashback reveals what brought Lena to Reese three days earlier. A neighbor, Charlotte Warren, called to say Hank was in bad shape. At Hank's house, Lena encounters a stocky, bald man with a red swastika tattoo beside a white Cadillac Escalade. Inside, she finds Hank emaciated and surrounded by drug paraphernalia, having relapsed into methamphetamine use after years of sobriety. Hank stuns her by claiming the tattooed man killed her mother. This contradicts everything Lena was told: that her mother, Angela Adams, died of an infection 13 days after giving birth, and her father, Calvin Adams, a deputy, was shot dead before the twins were born.
At the Elawah County hospital, Jeffrey and Sara meet Sheriff Jake Valentine. Valentine explains that the burning Escalade was found on the football field with a body in the backseat and that Lena was discovered on the nearby bleachers, bruised and silent, with her foot on a gas can. She has refused to speak, and bail has been denied. Sara stays alone with Lena, who manipulates her into removing her restraints by pretending to be fragile, then escapes through the drop ceiling and flees the hospital.
As they leave, a burly man with a red swastika tattoo confronts Jeffrey. Both he and Sara connect the marking to Lena's abusive ex-boyfriend, Ethan Green, a convicted neo-Nazi skinhead. The next morning, Jeffrey meets Nick Shelton, a Georgia Bureau of Investigation agent. Nick explains that the Brotherhood of the True White Skin is a violent neo-Nazi gang running methamphetamine through the Southeast, led by the Fitzpatrick brothers from New Hampshire. The red swastika is their emblem. Nick reveals that the previous Elawah sheriff was firebombed out of his home by the Brotherhood and confirms that Ethan's rival gang uses a black swastika, easing Jeffrey's fear that Ethan is behind events in Reese.
Meanwhile, Lena discovers a 1971 newspaper photograph showing her mother alive and holding twin babies months after Angela supposedly died. Hank refuses to explain. Searching his bar office, Lena finds letters revealing Charlotte Warren was Hank's Alcoholics Anonymous sponsee and Sibyl's secret lover in high school. Charlotte reveals another devastating truth: It was not Hank who accidentally blinded Sibyl by backing a car into her as a child, but Angela, who fled without checking on her daughter. The one thing Lena could never forgive Hank for, he never did.
Sara's autopsy of the Escalade victim reveals the body is a woman burned alive, not Hank. On Wednesday night, Hank's bar catches fire, and shortly after, Boyd Gibson, a local with a red swastika tattoo, is thrown dead through Jeffrey and Sara's motel window, stabbed with Lena's distinctive pearl-handled folding knife. Separately, Lena finds the body of Deacon Simms, Hank's longtime friend and bartender, beaten to death in Hank's attic, and conceals the discovery. Sara's autopsy of Gibson proves the fatal wound was made by a blade far larger than Lena's knife, confirming someone killed Gibson and planted the knife to frame her.
Lena visits Ethan in prison, but he refuses to share information and appears unconnected to events in Reese. On the drive back, her car is forced off the road by a white Escalade. Inside, she finds Charlotte bound and gagged, with the masked man holding a gun to Charlotte's head. Lena is forced to drive to the football field, where the man has an accomplice, Clint, inject Charlotte with drugs before dousing her in lighter fluid and dropping a lit lighter. This is the scene from the prologue: The victim is Charlotte Warren. Valentine arrests Lena on the bleachers.
Jeffrey finds Hank near death in his backyard, beaten and bound. Sara performs CPR, and they get him to the hospital. Lena calls Sara, distraught, warning that Jeffrey could suffer the same fate. Charlotte's husband, Larry Gibson, reports her missing, and Valentine finds birth certificate applications in Charlotte's belongings listing Hank, not Calvin Adams, as the twins' father.
After escaping the hospital, Lena conducts surveillance of a warehouse serving as the meth operation's hub, photographs transactions, and sends copies to a colleague as insurance. She turns herself in, and a lawyer gets the charges dismissed. Valentine resigns after receiving a death threat.
Jeffrey leaves for the prison while Valentine drives Sara and Lena to Hank's house. There, Lena spots a blood-type tattoo on Valentine's inner arm, a neo-Nazi leadership insignia she recognizes from Ethan's arrest file. Valentine pulls his gun, revealing himself as the true leader of the local meth operation and a Brotherhood member whose wife is the Fitzpatrick brothers' sister. He summons Clint and Fred Bart, the local dentist who also serves as county coroner, to stage a meth lab explosion that will kill the women and destroy evidence. Bart injects Sara with a sedative.
Bart then realizes Valentine has been setting him up as the fall guy. He shoots Clint dead and shoots Valentine before leaving with volatile chemicals heating on the stove. Lena, handcuffed to the unconscious Valentine through the sink's drainpipe, hacks through Valentine's wrist to free herself and drags the sedated Sara out moments before the house explodes.
Jeffrey confirms at the prison that Ethan has no Brotherhood connection and was calling Hank simply to torment Lena. He then discovers that Angela Adams is alive, working as the maid at the motel where he and Sara have been staying, aged beyond recognition by decades of meth use. Angela reveals that Bart started her addiction after Calvin's death, she blinded Sibyl while driving high, and she and Hank agreed the girls would be better off thinking she was dead. Angela refuses to see Lena.
In the hospital, Hank lies to protect Lena, telling her Angela died in a car accident years ago and admitting he took the blame for blinding Sibyl to spare the girls from hating their mother. Sara waits at home, having spoken with an adoption agency about a baby boy. Jeffrey arrives ecstatic. He opens the mailbox, and a bomb explodes, tearing off his right arm and ripping open his chest. Sara rushes to him, but the wound is catastrophic. His last words are a fragmented declaration of love. Jeffrey dies in Sara's arms on the street in front of their home.