The Alloy of Law by Brandon Sanderson (2011) Dragonsteel Entertainment 

Set in the world of Sanderson’s first Alloy series, this takes place about 300 years later.  The hero is from one of the upper families but has been spending his time in the roughs as a lawman.  His uncle and family died in an accident and ‘Wax’ must return to the city to take care of the family business that employees thousands.  The family is almost bankrupt, and a marriage has been arranged with a lower family that is wealthy.  During this, a group of robbers has been attacking trains and taking hostages.  When they take Wax’s fiancé, he must save her.