Friendless and hunted, Tessa takes refuge with the Shadowhunters of the London Institute, who swear to find her brother if she will use her power to help them. She soon finds herself fascinated by and torn between two best friends: Jem, whose fragile beauty hides a deadly secret, and blue-eyed Will, whose caustic wit and volatile moods keep everyone in his life at arm's length...everyone, that is, but Tessa. As their search draws them deep into the heart of an arcane plot that threatens to destroy all Shadowhunters, Tessa realizes that she may need to choose between saving her brother and helping the Nephilim save the world...and that love may be the most dangerous magic of all.