The lost metal by Brandon Sanderson

For years, frontier lawman turned big-city senator Waxillium Ladrian has hunted the shadowy organisation the Set – with his late uncle and his sister among their leaders – since they started kidnapping people with the power of Allomancy in their bloodlines. When Detective Marasi Colms and her partner Wayne find stockpiled weapons bound for the Outer City of Bilming, this opens a new lead. Conflict between Elendel and the Outer Cities only favors the Set, and their tendrils now reach to the Elendel Senate – whose corruption Wax and Steris have sought to expose – and Bilming is even more entangled. After Wax discovers a new type of explosive that can unleash unprecedented destruction and realises that the Set must already have it, an immortal kandra serving Scadrial’s god reveals that Harmony’s power is blocked in Bilming.