by J. E. Andrews
The Merged Worlds book 4.
Stacey Bowen, vampire, daggerwoman, runs into a strange kind of magic that only her daggers can defeat. Allied with the police, an invisible new friend, her wizard, Nash, and her artist friend, Angie, Stacey takes on this dangerous case. With new powers emerging, Stacey finds that her enemies aren't the only of her difficulties.