You'd have to chain them, if each is a unique boss. This will lead to some running here and there on the map. I'd suggest having Marko as the BBEG, on a later mish. Story-wise, you'd want to address the questions presented by the intro, as in:
Who are these guys? What do they (really) want)?
What is my role in repelling them? If this is a big city-wide invasion, I assume I'll be dealing with a piece of it. I would think it'd be "all hands on deck." If so what is happening in the world around me?
What's the twist? (a good story will almost always have one in there somewhere)
Speaking of, it feels like there's a connection between the contact and the bad guys. (other than it being his turf) If not, story still works, but personal angles, character motivations, etc., deepen the story aspect.
Good start!