It's an "epic game of deduction and reasoning" that is a hell of a lot of fun. The basic premise of the game:
You have x number of players. Some of these are mafia, some of them are town. The mafia know who the other mafia are, and who the town are. The town know only their own personal alignment. During 'day', every player casts a vote on someone to lynch. During 'night', the mafia kill people. Town win if they lynch all mafia. Mafia win if they kill all the town.