The Darkness Before Them by Matthew Ward

The first in an exciting, action-packed new trilogy from epic fantasy author Matthew Ward, The Darkness Before Them introduces readers to a world ruled by a dangerous immortal king, where souls fuel magic, and a supernatural mist known as the Veil threatens to engulf the land. These are dark times for the Kingdom of Khalad. As the magical mists of the Veil devour the land, the populace struggles beneath the rule of ruthless noble houses and their uncaring immortal king.
Kat doesn't care about any of that. A talented thief, she's pursuing one big score that will settle the debt that destroyed her family. No easy feat in a realm where indentured spirits hold vigil over every vault and treasure room. However, Kat has a unique gift: she can speak to those spirits, and even command them. She'll need every advantage she can get.
Kat's not a hero. She just wants to be free. To have her old life back. But as rebellion rekindles and the war for Khalad's future begins, everyone - Kat included - will have to pick a side.