Years ago at a school dance, a girl named Mary was accidentally killed by a brutish jock who was mad when she refused to make out with him. No one ever knew what happened to her, but legend has it if you say her name three times she'll come to get you. So three high school girls decide to test the odd's and carnage ensues.
Anyone who is afraid of what might be hiding under their bed -and I am - will get totally creeped out by the scenes of Mary crawling out from under the bed. Otherwise I'm not sure if there's anything that would be all that scary.