Clockwork Angel is a novel written by Cassandra Clare. It is the first novel in the Infernal Devices trilogy. Tessa Gray (one of the main characters), goes to London to live with her brother. When she gets there she is captured by two cruel twins who go by the name of 'the Dark Sisters' for six weeks until William Herondale (a Shadowhunter) comes and rescues Tessa. The book became a best-seller in the New York Times list, debuting number 1 on the children's bestselling list.