Here’s the description:
In a nightmare world where the things in the dark are large and hungry and humanity has been driven back to the tribal and savage, a man like Avery Belfour is an asset. Avery is a machinist, one of the few left with the knowledge to keep mechanical devices—in particular, guns—in working order. But being in such high demand comes with a price: Avery is kept as a prisoner under lock and key.
When a rival colony raids the compound Avery is kept in and breaks him out, Avery has a brief hope that his incarceration is over. But it turns out that his saviors have just as much need for his services and are just as unlikely to give him the chance to say no. He is dragged away to meet the dark and deadly Harrow, the leader of this new colony. Harrow is a hard man, made so by his circumstances, but Avery wants his freedom, and is willing to do anything to secure it.