A fun party we put on for one of our kids was a murder mystery dinner on a local train. Everyone on the train was "in on it" and the servers were actors too.
The kids loved getting dressed up and having dinner while getting to be detectives. I filmed the action so they could watch it all over again later that night at the slumber party.
If you don't have a murder mystery train in your town or city, you can host your own murder mystery dinner, they come in party packages. Oh, and don't forget to tape off the location of the murder with yellow caution tape. This really adds to the party flavor.