The Unseen (1980 film)

The Unseen is an American 1980 horror film directed by Danny Steinmann.

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. The grate of the vent slams down on her neck, killing her. At the parade, Karen leaves Jennifer and Tony to talk, and makes her way back to the house alonewhere she too is then attacked and killed by the unseen, as it attempts to pull her by her scarf 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 overyears ago in order to maintain the unnatural 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 the subservient 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. ........

Source: Wikipedia