The Mortal Instruments

from Yen Press:
Hanging out with her best friend, Simon, is just about the most exciting thing in Clary's life...that is, until she realizes there are people only she can see. But when her mother disappears and a monster attacks her, Clary has to embrace a world that she never even knew existed--a world full of vampires, werewolves, demons, and those who fight for the humans, Shadowhunters...