Two sisters, Jennifer [Barbara Bach] and Karen [Karen Lamm], along with their friend Vicki [Lois Young], encounter a friendly but shady man named Ernest [Sydney Lassick], the owner of a small-town museum near Solvang, California. He invites the trio to stay for cheap room and board at his sprawling farmhouse on the outskirts of town, where his wife Virginia [Lelia Goldoni] keeps house. Soon after, Jennifer and Karen head to the Danish cultural festival that Jennifer is covering, where she is reacquainted with her estranged boyfriend, Tony [Douglas Barr], who convinces her to linger and talk about their relationship.
Meanwhile, back at the house, Vicki tries to nap, but an unseen figure attacks her. The assailant pulls her toward a floor vent, and when she struggles to escape, the grate slams shut on her neck, ending her life. At the parade, Karen departs from Jennifer and Tony to talk, then returns home alone, where she is attacked and killed by the unseen force as it attempts to drag her through a basement vent by her scarf. Virginia, who has been in the barn slaughtering a chicken, soon discovers the horrifying scene and is left devastated.
Ernest returns to a shaken Virginia and reveals a dark family secret: he and Virginia are siblings, and he murdered his own sadistic father over twenty years ago to maintain their incestuous relationship. They keep their inbred son, sometimes called “Junior” [Stephen Furst], locked in the basement, where he is often beaten. Ernest plants the idea in Virginia’s mind that Jennifer must be killed to keep their web of lies from unraveling.
When Jennifer comes back that evening, Ernest lures her into the basement and locks her inside. She wanders the dim space, stumbling upon the bodies of Karen and Vicki. In the oppressive darkness, Junior, a childlike and mentally vulnerable presence, begins to interact with Jennifer in a troubling way. Ernest presses in to kill Jennifer, but Virginia, moved by a turn of conscience, attempts to stop him. A violent confrontation ensues; Junior, enraged by the sight, intervenes to protect his mother, and Ernest kills Junior with a brutal stab to the head.
Jennifer manages to escape the basement but is pursued by Ernest. Tony, who has returned in an effort to mend fences with Jennifer, helps but stumbles due to a leg injury. As Ernest closes in on Jennifer, Virginia shoots him dead. The film ends with Virginia returning to the basement to cradle Junior’s corpse, while Jennifer slips away into the night, leaving the unsettling memories of the farmhouse behind.
