Soul Screamers: My Soul to Keep by Rachel Vincent (author) (UK edition)

Kaylee has one addiction: her boyfriend Nash. A banshee like her, he understands her like no one else. Nothing – supernatural or otherwise – can come between them. Until something does. Demon breath. A potent paranormal drug which has the power to kill. Somehow the super-addictive substance has made its way to the human world. But how? Now Kaylee and Nash are racing to cut off the source and protect their friends, one of whom is already hooked. The trouble is, so is Nash…