The Vampire Trap by Ali Winters

When a series of murders breaks out across the city of Sangate, all evidence points to the most powerful vampire in the city.

Zadie vows to do whatever she can to stop the killer. Only the viscount is as charming and witty as he is handsome. The more time she spends with him, the less she believes he is the monster terrorizing the city. Zadie must uncover the truth before her growing feelings blind her, or she might wind up as the next to die.
The Vampire Trap is a spicy, New Adult, stand alone,novella set in the Shadow World: The Vampire Debt series.
It can be read independently from the main series and without spoilers.