13th Birthday Party

Hi~
Me and my bestfriend Emily are planning a 13th birthday party. We were thinking about a Hollywood Murder Mystery Party, but arent sure what to do. Any tips on planning a murder mystery? this is going to be a really big night to us, so it has to be good. Onbly about ten people are invited so the murder mystery cant be planned for 20 or 30. Maybe around 15 would be nice., thanks, abb `n` emm