What system would you use to run a totally normal but foolishness-friendly gameworld?

[Trekkin]

My best friend/co-DM and I had a rather crazy idea after watching A Bit of Fry and Laurie: a campaign world that is totally normal, with no overarching plot of any sort, until one day the PCs are approached by a wise old man who hastily explains they're the Chosen Ones needed to stop a great evil and save an unknowing world.

The catch, of course, is that the wise old man is either crazy or lying for his own amusement, and they're being sent on a wild goose chase into a totally ordinary world, with only the normal abnormalities. Players being players, I can't see them realizing this ex nihilo, especially if not let in on it out of character, and if my players are any guide they're more than willing to zero in on some kind of trouble and start getting into it, and their actions form the driving principle of a campaign it's surprisingly easy to prepare for.

I'm fairly sure there's an enjoyable campaign here in the form of an insanity-driven trip through a world with all the depth and intricacy of our own, but I have no idea what system to use to make PCs just that bit over the normal that they have a good chance of surviving player decision-making processes, but not so into the superhuman that it becomes really unrealistic. Is there any modern or near-future system that works well at that power level?

[erikun]

I tend to like World of Darkness for making generally human-level starting characters, although fairly competent ones. They'll probably end up becoming pretty strong if you keep handing them XP, though, and the players would likely become suspicious if you didn't.

[Arbane]

Unknown Armies might work for this.