In 1946, a woman is raped during a party on her father's island. Her dogs come to the rescue, viciously attacking her attacker.
More than thirty years later, two brothers, their sister, and their two girlfriends go out on their large boat on a large lake. One of the brothers is a rather disturbed individual, who fires a gun he has nearly pointed at his brother at point-blank range, among other things. They have some trouble navigating the boat at night, and come across someone stranded in his boat. They bring him aboard, and he's grateful. He tells them about the island they are near, where a crazy old lady lives with lots of dogs.
The psycho brother decides he wants to try driving the boat at night, though they had anchored already. He grabs his gun when they try to stop him. The boat runs aground and blows up, landing everyone on the island.
Though they had heard dogs barking, the only dogs them come across are skeletons. There's no sign of the old lady, and someone starts killing them off. It's no secret that the killer is the old lady's son, the son of the rapist, presumably. Though we never get a good look at him, a diary they find indicates he has acromegaly. Having that doesn't make a person a monster (André the Giant and Rondo Hatton, among others, had that condition). Evidently he is brain-damaged as well, or severely screwed up because of the way his mother raised him.
The movie is pretty derivative. I've seen quite a few movies where at some point a young woman pretends to be a killer's mother to try to save herself, for example. At a couple points, the good brother, his girlfriend, and his sister reminded me of Fred, Daphne, and Velma, respectively, from Scooby-Doo.
Many of the scenes take place at nighttime, and on the videotape, yes the picture is often almost completely or completely black. Evidently this was not true when the film had been projected, so it is probably a matter of a bad transfer.
