Milo lives in a steel cave within a man-made mountain of steel and concrete. He spends his days repairing the machinery that keeps the habitat livable and tinkering with the prosthetics that help his twisted body move about through the small tunnels and air shafts that are his world. He's as much a piece of discarded machinery as the equipment he keeps running. 
Given a chance at being someone different will he become a hero and live in the sunlight? The light beckons, but there are secrets buried in the ground. Ancient mysteries left by races that delved deep and stayed below. Maybe only a tunnel rat culd find them?
And thanks to the artist of that handsome rat for inspiration. Find more of her work here: https://www.deviantart.com/watch/memymine/deviations