Murphy's Law of Vampires (Love at First Bite Book 2) by Declan Finn

After saving Brooklyn from a nest of vampires, Amanda Colt and Marco Catalano are a little banged up. He’s been given a job offer to deal with vampires in San Francisco, and it’s a tempting offer – it would get him away from Amanda, his feelings for her, and get her away from the darkness inside him. When a death in the family compels Marco to move to the West Coast, they’re both left to fend for themselves. But when a creature known only as “Mister Day” leaves their world in tatters, they must once more join forces against the darkness. Only and “Day and ” is no vampire, but a creature beyond their experience. It will take the combined might of Marco, Amanda, and all of their allies just to slow it down. They have no weapons that can kill him. They have no ways to imprison him. To even fight him is death. But they have to try, or face the end of everything they love.