After a hotel reservation mix up, two sisters Karen and Jennifer, and their friend Vicki Thompson, meet a friendly, but shady character named Ernest Keller. Ernest convinces the women into accepting an invitation for cheap room and board at his large farmhouse where his wife Virginia also lives. Once there, Jennifer and Karen leave for the holiday parade fair which Jennifer, a news reporter, is reporting on. At the festival, Jennifer is met by her soon to be ex-boyfriend, Tony, who gets her to stay behind to talk about their relationship. Meanwhile, back at the house, Vicki prepares to take a nap in her room, but is attacked by an unseen figure. The unseen eventually begins to pull Vicki into a floor vent when she tries to escape. At the parade, Karen leaves Jennifer and Tony to talk, and makes her way back to the house alone—where she too is then attacked and killed by the unseen, as it attempts to pull her by her hair through a vent into the basement. Virginia, who had been in the barn slaughtering a chicken, soon after comes inside to find the bodies of both Vicki and Karen.
When Ernest arrives back at the house, he finds Virginia in shock. At this point, it is revealed through flashbacks that Virginia and Ernest are, in fact, brother and sister, and that Ernest had murdered his own sadistic father years before in order to maintain the relationship. It is also revealed that they have an incestual son named 'Junior' who has been kept locked up in the basement; the viewer also learns that Junior is often viciously beaten by Ernest. Ernest then convinces Virginia, who the viewer now realizes is taken advantage of by Ernest, that Jennifer must be killed upon her return, in order to keep everything under cover.
When Jennifer gets back, she is lured into the basement by Ernest, who then locks her inside. She wanders around looking for a way out, only to stumble upon Karen and Vicki's dead bodies. In a panic, she is confronted by Junior, who turns out to be a mentally retarded and infantile grown man; at this point, it becomes clear that in all likelihood he did not actually mean to kill Karen and Vicki. Ernest comes into the basement to finish off Jennifer, but Virginia, having had a change of heart, attempts to stop him. Ernest begins attacking Virginia, but Junior, enraged by the sight, intervenes to protect his mother. A fight breaks out between Junior and Ernest, while Jennifer escapes. The fight ends with Ernest gaining advantage over Junior, and knocking him in the head with a broken board containing a sharp, exposed nail, which causes Junior to collapse and die. Ernest then makes his way outside to hunt down and kill Jennifer. Just as she is about to be attacked, Tony pulls-up in his car, sees the commotion, and runs to help her, but trips and falls due to an existing leg injury. However, at the last possible moment, Ernest is shot in the chest from afar by Virginia. The film ends with Virginia cradling the dead body of Junior.
