I too have a plot for a story and i was hoping that it hasn't been done already, some help please?

Hey, i have this idea for a story i'm planning to write, its got the typical storyline of some people getting trapped inside their high school/college and since 'serial killer on the loose' and 'ghost haunting' has been done... i thought of making it kinda like an adventure cum fantasy plot...

The main character's find hidden treasure in the school... but i'm not talking about the typical treasure of gold, silver and jewels.... more like the secret of the school that has been protected for a long time that involves something (haven't thought much about that yet) and not like HP also where they find the Sorcerer's Stone that will grant immortality or anything....

Its a little confusing and still in the planning stages but i think this is a little different right??? if anyone has any other ideas to help make the typical plot of 'trapped in school' different from the rest, i'll be glad to hear them... and props to all!!! thanks a lot...