The setting is a once peaceful town which has been invaded by the dark forces of corruption - the Mafia.
The Mafia's sole purpose is to murder the productive citizens in their bed. They have free reign of the town at night, but by day they appear to be normal citizens.
As a response to these terrible events, the townspeople have hired a Detective, whose job is to remain disguised while attempting to root our the members of the Mafia.
Players are either townspeople, Mafia or the Detective. Who plays what role is determined by the pre-appointed "god". The diety walks around when all the players' eyes are closed and secretly assigns them different roles by tapping them on the shoulder various amounts.
The game takes place over the duration of several "days" and "nights". Play begins at the start of the first "day", and proceeds as follows:
Everyone discusses who might be in the Mafia. Formal accusations are make and eventually a consensus is reached on who to hang. The unlucky victim is lynched by the angry and paranoid mob of townspeople (or run out of town if you prefer the PC version).
Night falls. Everyone goes to sleep (by closing their eyes).
God tells the members of the Mafia to open their eyes. The members of the Mafia then select someone they will murder, by pointing at people until they all agree on one. The Mafia then close their eyes.
There are several variants on this. The mafia can know who each other are, or not, and they can vote together or not. All these decisions are usually left up to the God.
God tells the Detective to open his eyes. The Detective then points at a suspect. God nods "yes" if that person in the Mafia, or "no" if they are innocent. The Detective then closes his eyes.
Note that this phase still occurs even if the Detective has been killed. The Detective no longer gets any (useful) information because he is dead, but it keeps the townspeople in the dark as to whether the Detective is still alive or not.
God announces the coming of the morning, and the name of the luckless victim of nefarious Mafia activity. (It is tradition to make up some good/zany story about how the mafia accomplishes their foul deed). There may be no victim if the mafia aren't acting together and didn't agree during the night.
The townspeople, realizing that their previous council did not root out all the evil, return to step one and play proceeds from there.
The game is over when: