Story istance?

I'm creating an original project that speaks of discrimination, war and the misuse of religion. A city begins the macre of certain people, claiming that they're blots on the planet-and a colossal disgrace to the heavens. Two characters move into that city, believing that they'll have a rather peaceful time, but the city's not what it appears to be. It's perfect on the outside, but is actually riddled with blood and corruption. I wish to put a twist on the characters (turning one to the 'dark' side, for example). It'll be a combination of modern and fantasy elements, but not too dark or gritty! Could someone help me with the characters? I want both or at least one to overcome mive personal difficulties, all the while wrestling with the corrupt government/city. What magic could I instill into this story? Thanks!