In the affluent lakefront community of Cloverhill Lakes, Connecticut, three women's lives collide when violence shatters the town's veneer of safety. Regan Hoffman, a widowed mother grieving her husband Jack's death two years earlier on a business trip to Colombia, attends the annual Labor Day party with her close friends Andi Bennett and Sasha Blanc, a newcomer to the neighborhood. When Ally Whitlock, the party's unofficial coordinator, borrows Regan's car keys for an emergency ice run, the car explodes in the parking lot, killing Ally. Police discover an explosive device, and Regan realizes the bomb was meant for her.
One month later, Andi, remarried to Carson after a bitter divorce from Ray Davila, is embroiled in a feud with Tia Hainsley, Ray's new wife, who has filed complaints with code compliance and the homeowners' association over violations at Andi's property. Their latest confrontation turns physical. At home, Andi learns a bomb threat was made at the local elementary school: Someone left a kitchen timer in a box with a note reading "Bang. You're dead." Carson, unsettled by the threat and by a figure he spotted in the woods behind their house, persuades Andi to practice shooting along the fence line. When Carson steps away to take a call, Andi fires one more shot, walks to the fence, and discovers Tia's body on the ground behind it.
Paralyzed by shock, Andi does not call for help. Convinced no one will believe the death was accidental given her public feud with Tia, she resolves to conceal the body to protect her children, sixteen-year-old Roxie and ten-year-old Dez, from losing their mother to a murder charge. When Ray arrives the next morning reporting Tia missing, Andi consoles him while hiding the truth. Over the following days, she hides the body in an unused meat freezer in the garage and eventually transports it to a remote stretch of the Connecticut River.
Sasha carries secrets of her own. She has been visiting her ex-husband, Rafael "Raffy" Carro, a recluse with an alcohol addiction living alone in their old cliffside house. Years earlier, they were tricked at a Mexican airport into escorting an elderly woman whose wheelchair contained smuggled drugs. Raffy took the blame to protect Sasha, served three years in a Mexican prison, and never recovered. Sasha has hidden this history from her husband Tom, whose family runs the locally famous Blanc's Barbecue restaurant chain.
After the school bomb threat, Sasha discovers red construction paper in her sixteen-year-old son Drew's room with a cutout matching the threat's description. Drew has also been suspended and lying about his whereabouts. Using a GPS tracker, she follows him to Hartford and watches him visit a smoke shop. When she enters to investigate, men in the basement attack her, break her finger, and threaten her by reciting her home address. At Raffy's house, she notices Drew's backpack by the door, despite Raffy's claim that he has not seen Drew in months.
Regan makes her own unsettling discovery. At her daughter Hallie's school play, she sends a selfie to Andi, who notices a man resembling Jack in the background. Regan chases the figure to the Amtrak station, but he boards a train to Windsor Locks before she can reach him. She posts Jack's photo online, and a woman named Beatrice at the Bluebird Café near Windsor Locks confirms she recognizes the man as a regular. Soon after, an intruder breaks into Regan's basement and strikes her on the head. While recovering at Sasha's house, Regan finds a photo of Jack in Drew's backpack. Back home, she discovers a locked safe box that opens with a key from Jack's glove compartment; inside is a driver's license bearing Jack's photo under the name Patrick Finch. She receives an anonymous text: "Jack is dead. If you don't stop, you'll be next."
The threads converge when Drew confesses to Sasha. He and Roxie have been investigating the interconnected crimes. At the Labor Day party, Drew saw Raffy parked nearby, drunk and distraught. After the bombing, he feared Raffy was responsible. He and Roxie created the school bomb threat as a diversion, paying underground contacts for information. They cleared Raffy but kept digging, discovering Jack's true identity as Patrick Finch and his connection to Dominic Terreli, a man Jack testified against in a murder case. Through further research, they determined that Dominic is Tom Blanc's brother.
Ray then arrives at Andi's house in tears: Tia's body has washed up on the riverbank, and the cause of death is blunt force trauma, not a gunshot wound. Andi realizes someone else killed Tia and placed the body on her property. Unable to reach her friends, she searches Roxie's room and finds the teens' investigation folder linking Tom to the Terreli crime family. She drives to Sasha's house, but Tom is there instead. He sees the evidence and strangles Andi unconscious, binding her in a shed on Raffy's property.
Regan finally encounters Jack at the Bluebird Café when he appears in the back seat of her car. He reveals he was originally Patrick Finch, a financial consultant who witnessed the Terreli crime family commit murder at a resort in Mexico. After testifying against Dominic Terreli, he changed his identity. On his Colombia trip, the family found him and left him for dead. He survived but staged a false death to protect Regan and Hallie, then lived nearby off the grid. He sent the threatening text to halt her investigation. As they flee town, a hooded gunman pursues them and shoots Jack in the chest.
At Raffy's house, Sasha confronts Tom, who confesses at gunpoint. Born into the Terreli family, he reveals his father Al's real name is Murphy Terreli and the restaurant chain is a front for their operations. Tom was assigned to kill Sasha and Raffy when Raffy stopped making blackmail payments, but he fell in love with Sasha and secretly paid the debt. The family ordered him to eliminate Regan as punishment for Jack's testimony; the car bomb was his work, though it killed the wrong person. He murdered Tia because she found incriminating information on his phone, then planted her body on Andi's property and left evidence at Raffy's house to frame them both.
Andi escapes the shed using tools she finds inside and sends her location to Regan before Tom recaptures her. He shoots her in the stomach during the struggle. Regan arrives armed with a shotgun, finds Andi bleeding, and calls 911. She forces Tom inside, frees Sasha from a locked bathroom, and discovers Raffy zip-tied to a chair. Tom disarms Regan, but Raffy slides a steak knife within her reach, and she stabs it through Tom's palm. Sasha flees into the woods; Tom pursues and forces her into his truck. Driving recklessly to evade police, he crashes through a cliffside safety rail, and the truck flips onto a rock ledge below. Sasha survives. Tom, dangling from broken railing, begs her to pull him up. Her grip slips, and he falls.
Two weeks later, Tom, who survived the fall, is under police guard awaiting prison transfer, and his father has been arrested. Andi, hailed as a hero, privately carries the shame of having concealed and disposed of Tia's body. Regan reunites with Jack, who recovers at home with Hallie doting on him, but finds that two years of grief and trauma have made him feel like a stranger.
Six weeks later, Sasha has relocated with Drew and her young daughter Chloe to Tucson, Arizona, where Raffy is in a rehabilitation facility. She visits him daily, feeling hopeful for the first time in years. Then Tom escapes from the hospital and appears at the facility with a gun. In a final confrontation in the kitchen, Sasha grabs a pair of scissors and stabs Tom in the neck from behind, killing him. Raffy holds her on the floor as police arrive, telling her it is over.