A Shadow in the Reaping by Brynne Weaver

A siren who must stay silent to survive.
An executioner with a bounty he cannot kill.

Lu has been living a quiet, undercover life, a vampire hidden in the quaint village of Sanford. Afraid that her voice will give her secrets away, Lu has lived for years without words, speaking only to the one witch she can trust. Except, of course, when it’s time to hunt. When it comes to luring in her victims, no song is sweeter than Lu’s.
But when Lu’s hunt is interrupted by Ashen, a mysterious and striking Reaper of the Shadow Realm, it seems like fate has finally caught up with her. An executioner with a soul to claim, Ashen doesn’t realize he’s stumbled on the bounty of an immortal lifetime until it’s too late. As the two enemies are forced to work together to solve a crime that shouldn’t be possible, it’s more than just secrets that emerge between them.
With every moment that passes, Lu finds it harder and harder to live like a shadow among her enemies, especially the enigmatic demon she’s bound to. She might just be a little bored of living the quiet life. But for Lu, nothing is more inseparable than danger and desire.
…And there are few creatures in any realm more dangerous than Ashen.