Kate Garretson, Julianne Moore, works as a horse trainer on Echo Valley, a horse farm tucked in southern Pennsylvania. She is still reeling from the loss of her wife in a riding accident and struggles to keep the operation afloat. When money runs short, she turns to her ex-husband, Richard Garretson, Kyle MacLachlan, a lawyer who provides the $9,000 she needs to replace the roof but admonishes her for using the funds to help their daughter, Claire Garretson, Sydney Sweeney, a troubled young woman who has been in and out of rehab.
One night, Claire returns to the farm to visit her mother. Her reunion with Kate is interrupted when Claire's boyfriend, Ryan Sinclair, Edmund Donovan, arrives and the two have an argument; Claire leaves with him.
Several nights later, Claire returns wearing a bloodied shirt and confesses that she killed Ryan during the argument by pushing him and causing him to hit his head on a rock. In Claire's car, Kate discovers a corpse wrapped tightly in a sheet. Desperate to protect Claire, Kate drives the body to a nearby lake and sinks it with a heavy cinder block. She returns home and tells Claire she has taken care of the matter.
Some time later, after Kate pays Jackie the agreed sum, Claire disappears again. When Kate goes to search for her, she finds Claire with Ryan; Ryan pushes Kate to the ground and flees with Claire in his car, leaving Kate to grapple with the truth and her own fear.
Jackie Lawson, Domhnall Gleeson returns to the farm to press for repayment and learns that the body Kate disposed of belonged to a local addict, Greg Kaminski, who overdosed after Ryan supplied him fentanyl. With Leslie Oliver, Fiona Shaw helping, Kate had retrieved Greg's body from the lake and placed it in the barn's apartment after Kate started the fire, effectively framing Jackie. Jackie drugs Kate by sticking her with a hypodermic needle. Kate and Leslie devise a plan to burn the barn for insurance money, and Jackie temporarily moves into the apartment above the barn as a hired farmhand.
Late one night, Kate watches as Jackie fades into the night while she lights the barn on fire with a road flare, and he flees in his car.
The following morning, Kate is questioned by police, who inform her that the charred remains of a body were found in the rubble. Kate suggests they could be that of Greg Kaminski, whom she says was a friend of Jackie. Jackie, who denied knowing Kate, is brought in for questioning. It is revealed that Kate, with Leslie's help, had retrieved Greg's body from the lake and placed it in the barn's apartment just after Kate started the fire, effectively turning the scene into a case against Jackie. Kate intentionally left behind a metal pin from the road flare, which Jackie was seen purchasing via store cameras; police infer Greg overdosed inside the apartment, and that Jackie started the blaze to cover up his death.
Kate is cleared of suspicion, while Jackie is charged with the crime. Back at Echo Valley, Kate hires a crew to bulldoze and remove the rubble from the barn. Late one night, Kate is awakened by her dog barking, and finds Claire crying outside on the front porch. The two stare at one another through the front door window, leaving their future unresolved as the scene fades.
