The Clocktaur War Duology Tome 1
Clockwork Boys

When forger Slate is convicted of treason, she faces a death sentence. But her unique gift for sniffing out magic (literally) earns her a reprieve-of sorts. Along with a formerly demon-possessed paladin named Caliban, her murderous ex-lover, and an irritating sexist scholar, Slate sets off on a mission to learn about the Clockwork Boys, deadly mechanical soldiers from a neighboring kingdom who have been terrorizing their lands.
If they succeed, rewards and pardons await, but first they must survive a long journey through enemy territory to reach Anuket City. And Slate has her own reasons to dread returning to her former home. Slate and her crew aren't the first to be sent on this mission. None of their predecessors have returned, and Slate can't help but feel they've exchanged one death sentence for another. Her increasing closeness to Caliban isn't helping matters : for the first time in a long while, Slate might actually care about surviving.