I'm toying with using the time-honored tradition of "upside-down" (or would it be "bait-and-switch?")... anyways, in my upcoming game, there's going to be this noble. He'll be the one who brings the group together, and he'll be their major source of adventures/income. Of course, he's also using them to accomplish all sorts of various little odds and ends he needs done before he can claim a mythical artifact that promises total invincibility, which would then allow him to wipe out the town's ruling council and take over, using the assassin's guild he secretly sponsors as his army/enforcers...
It's all a little cliche, I know, but my players are all so used to linear plotting, it'll work... I think...