A tense morning unfolds for Cassie and David Osborne as a heated argument over his constant business trips lingers in the air. After David heads to work, Cassie decides to spend a few days with her sister, Joanne, taking their five-year-old daughter Samantha along for company. Their plans take a dark turn at a shabby gas station, where Roy Roy Scudder seems to help but instead engineers a breakdown and offers to tow them to his house. The moment they arrive, Cassie encounters Roy’s unstable wife, Georgina, who has been emotionally frayed since the mysterious death of her baby boy, while Samantha is pressed into the role of a “playmate” for Jill, Roy and Georgina’s other troubled child. The sisters’ delusions intensify as Georgina and Jill insist that the Osbournes are really Marlena and Donna, Marlena being Georgina’s widowed sister. Cassie overhears Samantha’s cries and Georgina blindly steers her toward the wrong room, locking her inside.
When Joanne realizes Cassie and Samantha never reach her house, she panics and calls the police, convinced David had a hand in their disappearance. David, meanwhile, begins a frantic search for his missing wife and child, while a nosy neighbor fuels the detective’s suspicions that he may have killed them. The tension deepens as Cassie endures confinement in a room without a toilet, forcing her to pee on the floor, a detail Roy misses only to have it later exploited. A large wrench Roy leaves behind becomes Cassie’s improvised tool; she hides it and later uses it to pry the door hinges. A photo of Marlena appears to resemble Cassie, a remark Roy makes before tearing the image apart, and Georgina insists on washing Cassie and addressing her as “Sis.” Cassie buys time by claiming she needs the toilet and cleverly hides the wrench in the toilet bowl. In a tense bath scene, Georgina bathes Cassie while Cassie secretly wields a pair of scissors, only for Georgina to seize them and cut Cassie’s hair to mimic Marlena.
The threats escalate as Jill escorts Samantha out under a rope around her neck, and Cassie must confront the danger while keeping her wits about her. A desperate struggle ensues: Cassie fights Roy with the wrench but is overpowered and dragged back to her room, where Roy, while looming over her unconscious body, grapples with a hallucinatory naysayer—an apparition of his dead father—urging him to seize the moment and insisting that he hasn’t had sex in a long time. Georgina’s reluctance to touch him stems from the memory of their “idiot child” Arthur.
David’s pursuit continues as he reaches Joanne’s house and learns that police blood reports have traced the crime to the Osborne residence. He grabs the keys to Joanne’s Volkswagen Microbus to avoid capture and follows a lead that Cassie and Samantha had taken a shortcut toward Turkey Creek, where the Scudder home lies. Arriving at Roy’s property, Roy Scudder claims he hasn’t seen them and would have noticed a classic Ford Thunderbird, while Jill’s mischief drops a doll David had bought for Samantha from a window. David realizes Cassie and Samantha are inside, but Roy ambushes him, strangling him with a chain and dumping him into a dry well.
That night Roy returns with drugged milk, his memory flashing back to smothering Arthur in his crib to silence him. He orders Cassie to change clothes in his presence, and when she refuses, he leaves to threaten her further. David regains consciousness in the well and eventually escapes, but Cassie, drugged and disoriented, slips and is knocked unconscious again. Roy confines her to the bed with chains, while Samantha finds a way to communicate with her mother, urging her to endure. Samantha escapes her room as Jill dozes, and Cassie encourages her to run toward the woods and seek help from the first car they encounter. Samantha summons courage but is briefly intercepted by David, who pulls her into the bathroom and then slips away again as Roy approaches.
In the woods, Samantha follows Jill’s guidance, evading capture by playing on Jill’s fears. She tricks Jill into taking her into the trees by crying, “Please don’t take me to the woods.” Samantha eventually breaks away, while in the house the truth about Marlena’s fates unfurls as Samantha’s father fights to reach them. David swims through swamps to hide from Roy’s shotgun, then races back to the house as Roy discovers Arthur’s opened grave and collapses in grief.
A pursuing Roy finally faces a renewed confrontation at the gas station where Cassie and David had stopped earlier. The officer there, who had recognized the Thunderbird and the car parts in Roy’s stash, heads to the Scudder home with orders. Roy ambushes him, ending the officer’s life, and resumes his assault on Cassie and Georgina. Cassie bravely reveals that Roy raped her, but Georgina remains skeptical, clinging to the Marlena delusion and speaking of Marlena’s supposed plan to call the police. The tension peaks as power is cut and a hurricane lamp lights the room; David arrives with a hacksaw and begins to free Cassie from the bed’s chains, while Georgina accepts that Roy’s crimes have been exposed and that it would be safer to leave.
As the struggle escalates, Roy is driven to frenzy by the hallucination of his father, and he shoots toward it—only to kill Georgina instead. In the final confrontation, Cassie manages to shoot Roy, uttering a quiet, defiant resolve as the danger ends with his demise. The next day, the Osbornes are reunited, though Jill remains in a somber vigil by the well, where she nostalgically drops Samantha’s doll back into the depths. > I love you Marlena.
