Ok totally mind blocked, here's the game, and you'll soon see where the problem is:

One of the players is a mimic hired to fix someone's relationships; part family therapist, part method actor, part shapeshifter, he's hired to go into someone's life and replace them, say what they need to say but can't, and cut out vicious cycles before they become unstoppable.

But because this relies on profound deception, getting revealed before you fix the problems will obviously make them worse. All interventions are done based on analysis that a few months after they are successful, the operation can be revealed, but until that point no obvious improvements will be seen.

Mechanically, it's a challenge-based game, where the mimic player goes through a series of scenes with different characters, based on a day planner visible to everyone, and he has to hit certain points of conversation within each scene, while avoiding certain topics and not seeming to extreme in any one character trait (more on that in a minute).

The other players don't know what he is trying to avoid, because each players character details are supposed to be kept secret, and their sheet gives them parallel goals about something they want the mimic to agree to, underneath the main reason they are meeting. This is supposed to be close to the argument topic but not too close.

All non-mimic players also have the job of evaluating the roleplaying of the mimic player at the end of each scene, by secretly voting which trait out of 5 he most exemplified. If there are more than three votes in one trait suspicion builds, up, and with more than three strikes of suspicion, the game is over.

This is a cheat to create complex characterisation, by requiring people to balance ambiguously between five different styles; similar to the renaissance painting technique for emotion. I was reminded of the idea from a thread including a bit about good old skills/stats balance, with the idea that each task-type in the game should have 5 aspects, corresponding to the different stats. I twisted the idea of balance around so that it becomes the main roleplaying challenge.

Also there is the rule that the mimic has done his research, and can't be caught out by backstory, so this is a great opportunity for sliding in background details about the future world, although any of the other players can gainsay one of those additions if they think it messes with their character, and ask for a different version. This would probably be done with raising cards, like but separate to the voting cards, so as not to mess up the flow of conversation.

There aren't any times on the day planner thing, and the mimic player has control of pacing. He will want to manoeuvre the conversation around to the important topics, but not spend too long for risk of hitting touchy subjects.

Tuning?

Perhaps the mimic can go for varying levels of success? By saying more stuff? Perhaps the thresholds for suspicion need to be changed? Perhaps everyone should keep track of the agreements they have made so they have to keep them in later conversations. And perhaps other players should have some kind of taboo mechanic to inhibit them bringing their requests obviously into the open..

The problem of the game is that although I know structurally what sort of thing should happen in this game, and that once I get about two of the characters I can hopefully build from there, I've got a total blank on creating characters, any at all!

The week has come and gone as I've read short stories, newspapers, chatted to friends about it etc and still come up blank, so I thought I'd just put it up here, devoid of it's meat.

The ingredients?
Doctor Mimic
A thread about werewolves and social reward cycles gets gatecrashed by the werewolf parlor game, but gets me thinking about knots of relationships and evading detection
http://indie-rpgs.com/archive/index.php?topic=16791.0
And a thread about someone's incredibly elf-centric fantasy game, that includes the 5 stats for 5 actions thing, which I repurposed.
http://indie-rpgs.com/archive/index.php?topic=18279.0

And why is this a last chance game? Because in character it's your first and only chance to get things right, and out of character, it relies on hidden information to allow players to create a challenge for each other neutrally, because they do not know the criteria for success. Once you play the game you reveal the specific characters and the game is permanently changed.