April Fool's Day just happens to be the birthday of rich college student Buffy (Deborah Foreman), so she invites a group of friends from Vassar over to her family's island getaway to spend the weekend partying.
Though some practical-joke shenanigans on the ferry over from the mainland lead to unexpected bloodshed and put a damper on the festivities, Buffy unleashes a flood of more benign pranks on her guests, setting a tone of giddy abandon. With plenty of randy guys and gals on hand and no parental supervision, it isn't long before drunken escapades ensue.
As the weekend progresses, however, guests begin to disappear mysteriously, and before long Buffy and friends find themselves huddling in terror in their remote getaway. The next ferry isn't due until Monday, and the partygoers aren't sure whether any of them will make it that long.