So this may come out as too much of a retread, but I've been toying with an idea for a mystery/horror themed game. What I'm thinking:

Characters are transported into an empty city. It is a closed circle, the gates are locked tight, and there are no powers here. It's not just that their needs are all magically met - eventually, someone will notice that while there's food around, no one is getting hungry or thirsty. Sleeping is done out of habit, but that, too, is optional. Food and such is available, but not an unusual amount at once. Certain things DO seem to get restocked, but it very obviously comes from stores in the castle. They must fill in a role: worker, artisan, noble, etc. This is not optional, and if they are observed departing from the role, there is punishment.

However, none of that is the point of the game. The point of the game is the weekly masquerade ball, held in the castle in the center of town. All characters are required to don their finest clothes and a unique mask, and join the festivities in the castle. Exactly what the festivities, the queen decides. She in particular is never seen without her mask; she is cold and sadistic and her party games match her disposition. Naturally, she's also the one who's gathered everyone there to begin with. She may transform the party-goers, often in permanent ways, or toy with their thoughts and feelings against their will. Maybe sometimes she just slips poison into the wine, and the antidote is hidden in the castle, good luck finding it, etc.

Three options: people are drawn to the castle whether they want to be or not, and may or may not even be aware of it until after they arrive; people aren't forced at all, but monsters come out in the city during the masquerade (so maybe the queen is trying to protect people?); people are compelled in some fashion (or not, even), but people who resist and/or people who just don't want to come are taken by the queen's personal guard.

This relates to the punishment aspect. The queen's main form of punishing people who don't comply to her will is to have their mask permanently affixed to their face. Or at least semi-permanently. This can be reversed, but until you figure out how, good luck trying to pry it off your friend. What happens while they're stuck like this? You get to have fun playing a brainwashed puppet. Now, how exactly has three options, too. Whether or not we choose one, or modify these (they almost certainly need at least some tweaking), or try to combine a few would depend on what people wanted and such. One is that people who this happens to are essentially forced into their role. They act out their position in the city mechanically and will ignore interruptions at all cost. They will not become violent; they simple ignore stimulus that is not related to their task and try to keep performing it. When these citizens go to the ball, they participate eagerly in events and do not seem to notice anything wrong. Two is that they themselves get drafted onto the queen's guard, helping to keep other people in line and seemingly not remembering anything about their past lives.

Three may seem like an odd sort of punishment, at first. A permanently masked character would be taken into the queen's inner circle, one of the odd noblemen and ladies that surround her and see to her desires on a regular basis. They will help the queen as she sees fit and participate in masquerade events eagerly, evidently delighting in whatever harm they might inflict on former friends. Option two may be and option three would definitely be more of a "re-education" thing. They would be more like warped versions of themselves, apparently now buying into what the queen wants and gleefully doing her bidding. You'd essentially be playing one of the villains, if you liked. Again, all of these options will be reversible, but you also don't HAVE to get it reversed or you could have it take a while. Characters who die would also experience this, rather than staying dead permanently.

Outside of this, in their free time, characters can fulfill their duties as "citizens," or  try to figure out what's going on when the queen's guards aren't looking.

There IS a sort of long-term plot that players will be able to figure out, in terms of "what's going on/why/how do we stop it?" These are answerable questions and the game may not even run that long, though if people liked it, it could go in rounds or something.