For my 13th birthday, I am planning a murder mystery party. You could just use a murder mystery game, (I suggest University Game's murder mystery sets), but I decided to write my own so it would be more personalized. Because I love ballet, I chose to create the mystery "Corpse de Ballet" as a play-on words. Before the party, send out invitations telling each guest about the event and which character they will play. Decorate your house like a theater. Guests arrive in a grand entryway (they wear nice costumes, like thier characters), can sit down in an auditorium facing a stage, get food and drinks at the "concession stand", etc. Each guest recieves a script  and the murder begins. First tell everyone how the mystery works before things get   underway. When people are not acting, they can mingle, eat at the "concession stand", and do theater and ballet-related activities. In the middle of the party, I will ask everyone to stop what they are doing and come to the "auditorium" so that they can  watch a performance. This is comprised of any guest who wishes to do an act. I suggest the host do one (I am doing my solo to Giselle because it is ballet-related). At the end of the party, the murderer will be revealed. If someone guesses the murderer, they can get a small prize.