When sixteen-year-old orphan Tessa Gray's older brother suddenly vanishes, her search for him leads her into Victorian-era London's dangerous supernatural underworld, and when she discovers that she herself is a Downworlder, she must learn to trust the demon-killing Shadowhunters if she ever wants to learn to control her powers and find her brother.

When seventeen-year-old orphaned shapechanger Tessa Gray is kidnapped by the villainous Mortmain in his final bid for power, the London Institute rallies to save her, but is beset by danger and betrayal at every turn.