Spencer Green is normal-compared to most New Yorkers, anyway. She goes on a run in the mornings, washes her clothes at the local laundromat, and can hail a cab like a pro. On a night spent wandering the streets of New York, she comes across the Pandemonium Club. Drawn inside by something she can't explain, Spencer-literally-bumps into a teenaged boy armed with a multitude of weapons. Following him, she encounters three more strange teenagers and is witness to an unimaginable horror-an attempted murder. Now, Spencer is being stalked by those same teenagers that call themselves Shadowhunters, who explain to her the existence of a world both beneath and aligned with our own. The Shadow World is dark and dangerous, filled with vampires and werewolves and demons. Spencer cannot turn back now, cannot go back to her normal. She must stand and fight to protect her new friends and the mundanes threatened by the mysterious Valentine. And she must find the Mortal Cup before he does.