City of Bones by Cassandra Clare (The Mortal Instruments #1)

When Clary Fray heads out to the Pandemonium Club in New York City, she hardly expects to witness a murder. Much less a murder commited by three teenagers covered with odd markings. This is Clary's first meeting with the Shadowhunters, warriors dedicated to ridding the earth of demons--and keeping the odd werewolves and vampires in line. It's also her first meeting with gorgeous, golden-haired Jace. Within twenty-four hours Clary is pulled into Jace's world with a vengeance, when her mother disappears and Clary herself is attacked by a demon. But why would demons be interested in an ordinary mundane like Clary? And how did she suddenly get the Sight? The Shadowhunters would like to know....