Clockwork Angel is the first book in The Infernal Devices series by Cassandra Clare. The series is a steampunk-esque prequel to the New York Times bestseller The Mortal Instruments. Taking place in Victorian London, the book follows its warlock protagonist, Tessa Gray, as she goes to England at a request from her brother, Nathaniel Gray. She's taken captive by The Dark Sisters, who tell her that in order to see her brother again, she must marry someone called The Magister.