It is an interactive role-playing game, that involves solving a mystery which is based on clues at the scene of a staged crime.
Each party guest dresses up and plays a character involved in the mystery
During the course of the party, everyone uses their master sleuthing skills to find out who the Murderer is.
(The Murderer, of course, schemes and plots to avoid detection!)
These games often include other plots, and everyone becomes embroiled in a hilarious time of scheming, plotting, backstabbing & blackmailing each-other.