From the introduction:
In Leave or Stay players take the role of people from the same town or city. Some of these people left a while ago but are now back, some of them never left. During the game you will have a series of discussions with the other players dealing with how each of you perceives the town and your role in it now that it’s changed.
In order to play you need from 8 to 20 players, ideally from different age groups, the printed handouts, a name tag for each of the players, writing tools and about 2 hours of time. Everybody should either read or familiarize with the Safety and Playing the Game chapters before the game, so that everybody can both enjoy the game without stressing about not knowing what to do or explaining the rules during the game itself.