Irregulars — Nicole Kimberling

It's a secret international organization operating in cities on every continent. It polices relations between the earthly realm and those beyond this world, enforcing immigration laws, the transfers of magical artifacts, and crimes against humanity.
The agents who work for the NATO Irregular Affairs Division can't tell anyone what they do, or how hard they work to keep us safe. It brings a colorful collection of men together:
Agent Henry Falk, the undead bum. Agent Keith Curry, former carnivore chef turned vegetarian; Agent Rake, Babylonian demon with a penchant for easy living; and Agent Silas August, uncompromising jerk.
Four cities, four mysteries, four times the romance. Is your security clearance high enough to read on?