I think it sounds like a great mission...As far as motivation,,let me get a little "Hollywood" here for a moment. How about this.
You are trained Government assassin...You have a Brother back home who has moved with his wife to a small town and joined the local law enforcement agency. After being on the force for a while, he discovers that most of the Police force, as well as, some of the local High ranking public officials are in league with a local biker gang. He discovers that the dept. he is working for is not only sharing in the profits of the biker gangs drug & arms trade, but are also helping to eliminate the gang's competition. He decides that since no-one can be trusted locally, he will turn to the feds. But before he can do that, he is out one nite with his wife, and comes across a roadblock. As he pulls up,he notices several armed bikers, and a few of his fellow officers, including the chief. He tries to escape,but they open fire, killing him and his wife....Would make for a nice intro I think.......Anyway....the mission Idea sounds great, and I love that addon pack....Good luck with it.