In the third installment of The Mortal Instruments series, “City of Glass,” written by Cassandra Clare, we follow Clary Fray on her perilous quest to save her mother in the City of Glass. Simon a vampire immune to sunlight is being held captive by the Shadowhunters in the meantime. Valentine is threatening to wipe off the Shadowhunters so they might want to consider allying with the Downworlders their enduring foes.