Slayer in Lace by D.D. Miers

Proper. Polite. Utterly ruthless.

Emma Clearwater isn’t your typical lady and the revolver holstered under her skirts proves it. Emma is a slayer. The last in a long family legacy of those who protect the world from a powerful race of dragon shifters with enormous amounts of magic, the dragonborne.
When a slayer turns up dead, the fragile truce between the dragonborne and the slayers shatters and retribution is on the slayer’s to-do list. Fierce and handsome, dragonborne Callom Smythe is the heir to his father’s throne. Determined to uncover the true culprit trying to frame his people, Callom aligns himself with his mortal enemy.

But when these two adversaries meet, an unexpected desire forms. History forbids their romance; while destiny demands it. As darkness grows and more bodies turn up, they’ll have to trust each other to defeat the shadowy creatures that prowl Victorian New York.