Thaniel, just seventeen, is a wych-hunter. Together, he and Cathaline–his friend and mentor–track down the fearful creatures that lurk in the Old Quarter of London. It is on one of these hunts that he first encounters Alaizabel Cray. Alaizabel is half-crazed, lovely, and possessed.Whatever dreadful entity has entered her soul has turned her into a strange and unearthly magnet–attracting evil and drawing horrors from every dark corner. Cathaline and Thaniel must discover its cause–and defend humanity at all costs.