Demon’s Mark by T.F. Walsh

As a half-demon, Cary has survived a lot… but this love thing might be her undoing.

Levi Walker, master demon hunter, is on a mission to find the demon bastard who killed his best friend. As he finally tracks down the beast, he’s suddenly distracted by the newest Argos recruit – the sexy vixen who also broke his heart – and the battle takes a deadly turn. Now with the recruit in the beast’s sights, both she and Levi are instantly marked for death.
If Cary Stone’s secret is revealed (she’s a demon half-breed, after all), she’ll be thrown straight into Hell. After a lifetime following her father’s advice – never let anyone get close, never stay too long in one city, and ALWAYS work alone – in the past year she’s broken all the rules.
Not only did she get a job hunting demons, she also fell in love with the most badass hunter of them all. Oh and, if things weren’t interesting enough, she managed to grab the top spot on the hit list of the biggest mercenary in Hell. Yeah, shit just got real.