The Final Empire by Brandon Sanderson (Mistborn #1)

A thousand years ago evil came to the land and has ruled with an iron hand ever since. The sun shines fitfully under clouds of ash that float down endlessly from the constant eruption of volcanoes. A dark lord rules through the aristocratic families and ordinary folk are condemned to lives in servitude, sold as goods, labouring in the ash fields.

But now a troublemaker has arrived and there is rumour of revolt. A revolt that depends on a criminal no-one can trust and a young girl who must master Allomancy - the magic that lies in all metals.

Book by author Brandon Sanderson.