Alternatively, though it's a little late, one could have the city being invaded by domestic terrorists, anti CTos forces. They could either be primary antagonists or yet a third party.

The interesting thing is that they probably have similar goals to our Vigilante group, bringing down the CT grid, but are much less concerned about loss of life. It could start out with a "frenemy" angle and then explode into full mad on hate.

Use it... or not :)