Clockwork Heart Series by Dru Pagliassotti

A steampunkish romantic fantasy set in Ondinium, a city that beats to the ticking of a clockwork heart. Taya, a metal-winged courier, can travel freely across the city's sectors and mingle indiscriminately among its castes. A daring mid-air rescue leads to involvement with two scions of an upperclass family and entanglement in a web of terrorism, loyalty, murder, and secrets.

Taya, the metal-winged icarus whose investigation helped defeat a plot against Ondinium and its populace, is assisting her exalted husband Cristof Forlore on his first ambassadorial mission... moreTaya, the metal-winged icarus whose investigation helped defeat a plot against Ondinium and its populace, is assisting her exalted husband Cristof Forlore on his first ambassadorial mission. They must learn about Mareaux’s experiments in airship technology and determine whether the ostensibly scientific vehicles might be used for warfare — a taboo for Ondiniums, whose domination of the air is tempered by a deep cultural abhorrence toward airborne weapons after the devastation of the Last War a thousand years ago. less

The conclusion of the Clockwork Trilogy, in which Taya and Cristof are sent to Alzana to return the captive airship crews and negotiate for peace with King Quintilio. As international tensions escalate, war is declared on Ondinium, striking at its massive metal heart and resulting in the undoing of Ondinium s isolationist policies as it accustoms itself to a world where it no longer holds military superiority."