Hiding In The Shadows

I remembered an old concept I came up with back in 8th grade (I'm in 12th now haha) and I just want to develop on that again :)
Basically the story is about a couple of boys when society has crumbled to the ground and everyone is left to fend for themselves. The population has divided between the rich and the poor, those who live in the light and those who live in the dark. Many people almost dehumanized at this point. What happens when those two classes collide, a sickly rich boy named Sage and a small, thin poor boy named Mathew.