City of Fallen Angels is the fourth book in the The Mortal Instruments series by Cassandra Clare. The series was meant to end with City of Glass; it was announced in March 2010 that a fourth book would be added, with Cassandra Clare later saying that she views this as a "second trilogy" in the series. The book was released on April 5, 2011.
The book follows Simon's difficult transition into vampirism. Simon receives an offer from a vampire named Camille Belcourt who claims to have been usurped by Raphael. She says that if Simon joins her side as the Daylighter, then he will finally earn his place in vampire society. After his meeting with Camille, he returns home worried about what his mother will think as she has been suspicious since he went to Idris (City of Glass) and did not return for almost two weeks.