If you really can't think of anything creative or original, then work at developing your writing style really effectively, so that you present a cliched idea really really well.
Take a look at a variety of crime fiction compositions; they might give you a few ideas on how to write a variety of crime fiction texts. Just be careful for the HSC. The composition might not be a story.
my formula is a mafia story with generic mafioso characters including a don, capo's and their families and then a hell of a lot of blood, rape, violence, sex and torture, in the most horrifically descriptive form i can think of.
gets me full marks every time. honestly, violence is the way to go, not parody.