Jessica Chambers confronts her husband, John Chambers, over his affair with one of his students, Vivienne Ballard. Reluctantly agreeing to end the relationship, John commits to a family getaway at a remote plantation house along with their 14-year-old daughter, Anna Chambers.
Upon their arrival, Jessica insists that John prepare veal cutlets for dinner, despite his preference for hamburgers. In town, Anna encounters the charming yet peculiar local boy, Isaac, who flirtatiously engages her. Meanwhile, the store’s owner, whom Isaac refers to as his Grandpappy, casts a wary glance at John when he claims he couldn't find veal, despite its abundance. This interaction culminates in an ominous note added to John's receipt stating, “You are being watched by the devil.”
Back at the house, they find Jessica attempting to unlock a mysterious door which remains stubbornly shut. When Isaac later invites the family to dinner with his Grandpappy, the tension rises as Jessica exposes John's deceit about his shopping trip, which prompts her to accept the invitation out of spite.
John and Jessica's evening becomes fraught with conflict when Jessica expresses her apprehension about dining with strangers and confronts John about the threatening note. Their heated argument spirals into deeper marital issues, yet reconciliation follows John's vow to end his affair with Vivienne. Just as they decide against dinner due to Anna’s sudden nosebleed, Isaac returns with his Grandpappy, insisting on preparing the meal at their house.
As the evening unfolds, weirdness takes center stage—Isaac exhibits strange magical talents, and Jessica grows increasingly anxious over his intense flirtations with Anna, transformed by her own worries. A sudden series of events—Anna's fainting spell and the enigmatic presence of an unseen animal—heightens the family's fear.
Grandpappy, while in the kitchen, inadvertently reveals that he isn’t Isaac’s real grandfather. He claims to have taken Isaac in after the boy mysteriously appeared from the swamp one summer, stating that Isaac doesn’t seem to age. The atmosphere turns sinister when Grandpappy plays a recording of John professing his love to Vivienne, leading Jessica to realize the truth behind John's lies in the face of Isaac's brazen behavior.
The situation intensifies and culminates when Grandpappy threatens Anna, pushing Jessica to pour gasoline over Vivienne's car to protect her daughter. As fate would have it, a firefight ensues and ends fatally for Vivienne, leaving Jessica grappling with the explosion as a chance to confront Grandpappy.
In a chaotic climax, Jessica finds her husband in the grips of a wolf attack. As John dies, he whispers words of love for Vivienne, leaving Jessica to fend off the nightmarish chaos surrounding her. Isaac's reveal comes in a cruel twist, disclosing that he was meant to kill her while preparing to escape with Anna. The chaos culminates when Jessica shoots Isaac, questioning his true nature even as he claims to embody both demon and angel alike.
Finally, Jessica and Anna make their escape to a sheriff's station, but the horrors of the night don't seem to conclude—Deputy Torres reveals the shocking truth that the house is nonexistent. A disturbing video camera found in the patrol car shows the ghostly specters of Isaac and Grandpappy, with Torres warning Jessica about the dangers of speaking out against their infernal nature. Embracing the second chance at life, Jessica and Anna drive away, haunted yet determined never to return to that cursed bayou.
