Fang Me (The Demon Underground Urban Fantasy Series)

Part human, part succubus, and one bad decision away from losing it all. San Antonio's vampires want it. Its demons want it. And at least one of them is willing to kill teenage Slayer Val Shapiro to get it. The Encyclopedia Magicka—the only spellbook of its kind, powerful enough to doom the city in the wrong hands — is still missing, and Val's the one expected to track it down. Simple enough. Except Val's powers come with a catch she only just discovered: she keeps them exactly as long as she keeps her hands off Shade. And with a brooding shadow demon boyfriend who keeps feeding the lust demon living rent-free in her head, that's getting harder by the day. Give in, and the strength, speed, and healing that make her the Slayer are gone—for good. Now Val has to recover a stolen book everyone's hunting, survive the vampires and demons who'd kill for it, and figure out who she actually wants to be—before someone makes the choice for her.