Help creating a MYSTERY play!?

Question:I'm in charge of forming a mystery story for a group of teens. I'm having a complete writer's block and cannot think of any ideas. I'm wondering if anybody knows of any good plots. However, the ending has to be a secret, because some people of the audience have to guess the motives/killers/etc.

Best Answer - Chosen by Asker: I'm in charge of forming a mystery story for a group of teens. I'm having a complete writer's block and cannot think of any ideas. I'm wondering if anybody knows of any good plots. However, the ending has to be a secret, because some people of the audience have to guess the motives/killers/etc.

A group of students meet in a haunted house. One by one disappear . They don't know who is doing it. Nobody dies. Make this a take off on slasher movies without the slashing.
With only one left, everybody shows up and yells surprise!!
it's your birthday.