This campaign is for Rifts. It's not a full campaign, but it could easily lead to one. Read on to find out exactly how...
Background: I came up with this campaign idea after reading the article on the Operator O.C.C. in Rifter #5. An excellent article and a must read for anyone. The characters should start at a low level, probably level one. The party needs at least one "underground agent". By underground agent, I mean something like a Forger, Operator or other literate person who the CS feels pose a threat to them. This character is likely to have set up shop somewhere in the Burbs (either as a doctor, book lender, or mechanic) secretly. The other characters should probably be something common to the Burbs (city rat, vagabond or possibly another scholar) and are regulars at the shop. They might run errands for other citizens and such tasks so they can earn their living.
The campaign starts as the character owning the shop and at least one of the other PCs has showed up (perhaps the other PCs are already at the shop and the last character shows up). The last PC was unknowingly followed by the ISS. Only minutes after the other PC enters, the place is raided.
GM Note: Be nice to the player characters. Most likely they won't be in armor or will only be in Plain Clothes armor, so don't hit 'em with anything too horrible (like a plasma cannon). There are a couple possibilities here. First, the PCs could escape, in which case they're fugitives on the run. This could lead to a campaign of survival against one of the ISS fugitive retrieval units or any of the numerous bounty hunters at their disposal.
Second, the PCs could be captured. This could lead to the CS holding the PCs in prison (if they're vagabonds or city rats) or offering them a position (if one of the more scholarly O.C.C.s) in the ISS/Military. If some of the players refuse and some accept the offer (or some are being held anyway) it could lead to a prison break and who knows what else. If everyone accepts, what does the CS have in store for them as the newest additions to his war machine?