Two weeks after the events of the previous novel, Jace and Clary meet again and Clary discovers that Jace has been combined with her evil brother Sebastian. The Clave is after Sebastian but there is no way to harm one without harming the other. Realizing she has no other choice, Jace decides to gamble with fate and take up the Seelie Queen's promise. However the price may be more than she bargained for.