Boundary Born (Boundary Magic #3) by Melissa F. Olson

Something wicked is at work in Colorado’s supernatural community. Vampires are being paralyzed or killed with poison…a weapon favored by witches. This offense threatens to break apart the already-fractured alliance between witches and the undead.

The state’s cardinal vampire, Maven, summons boundary witch Allison “Lex” Luther to stop the killing before it ignites a war. Lex has barely started investigating when she gets another surprise: the biological father she’s never met arrives on her doorstep. He has answers to all of Lex’s questions about her bloodline, but getting those answers could mean betraying the life she’s already built.

Then the next vampire is poisoned—and this time it’s Maven herself. The new evil that hunts Lex is powerful and ruthless enough to stop the strongest supernatural creature in the state. In order to find such a killer, Lex will have to face down her own birthright and call on every ally—both living and dead.