Current ideas (mine first)
I mean, if you get called to the scene where a little girl has been abducted from a bedroom, you go find the little girl. But if you look between the lines, and realize that the reports of missing pets has skyrocketed, and there's a local ghoul gang, what do you do? In my mind, in this game, everyone would get together, and go do a little ass-kicking off the books. Not the SWAT team, not special forces, but good, honest, street cops.
Internal forces within Lonestar (policeman's union, secret fraternities, factions trying to gain power within the corporation, texas vs west coast, etc.), Mob ties (either to one of the characters, or a 'friend of a friend', or a setup), Internal Affairs Investigations (always a problem, especially when they execute a witch hunt trying to pin a crime on one of your characters to push attention away from a famous officer - maybe based loosely on a certain famous ork character concept), or maybe just a drug crazy that local cops have to deal with.
Eratosthenes (my fellow gamer): What if the street level cops realize those above them are trying to 'discourage' investigations, or just burying investigations. Maybe the street cops have been reporting murders to the detectives...but nothing ever gets done, and the cops are told to not talk about it? That would be a good impetus as to why the street cops might have to go outside the lines, as it were. Maybe the killer's a relative of the commish, or several of the higher ups are part of humanis, and enjoy the ork killings.
black magic/toxic spirit cult.
plain old corruption. Human trafficking that gets overlooked (lots of evil to be thwarted there), involving the mob/triads/etc. Or maybe a gang turf war, with the cops being told to work certain sides harder than others.
Maybe the cops get into a Real Bad situation (stumble upon a ghoul warren/vampire den, etc.), and are saved by some powerful NPC, who wants a favor (covering things up, finding things out, etc.), which leads them more and more into the NPC's thrall.
(Mine again) Play the corruption angle a little harder- a bunch of people trying to do the officers 'favors,' and then after it's been accepted, they learn who is pulling the strings? It could even work with inter-department favors, Humanis or Brotherhood of Sauron cops trying to get people to look the other direction?
Those are the starting ideas- knock anything loose?
-kv