(Yes, I know...a "horror movie" retelling of Shakespeare's The Tempest. And yes, I know about Forbidden Planet, so stop telling me my ideas are unoriginal! I just thought a "slasher movie" version of one of Shakespeare's plays would be cool, OK?
A group of teenagers/twentysomethings and their wealthy parents are the only survivors when their cruise ship washes up on an uncharted island after a storm. Wandering about the island, they get feelings of an unseen presence observing their every move. Like an unstoppable slasher, the being hunts them.
One of their number, Ferdinand (who calls himself "Fred" because it sounds less effeminate) discovers a beautiful girl on the island, and after a talk learns her name is Miranda. He also runs into her father, John Wayne "Duke" Prosper, who possesses weird superhuman powers...including, it turns out, the ability to summon the storm that sank the ship in the first place!
Duke tells his story: he was once mayor of Milan County, until he was framed for a crime he didn't commit. He and Miranda were driven out of town by rioting townsfolk, and got away on their houseboat. Then their boat washed up on the island, where they discovered a wrecked spaceship. Experimenting with the ship's technology gave Prosper his powers, and there was also a survivor: a brute named Caliban.
Prosper turned Caliban loose on the wealthy old men who framed him, but now Caliban is also hunting their children -- Fred's friends! Fred and Prosper will have to put aside their differences to stop Caliban.
So, whaddya think?