Sixteen year-old Tessa Gray moves from America to London to live with her brother after her aunt and guardian die. At the dock, Tessa is not met by her brother but by the Dark Sisters. The Dark Sisters kidnap Tessa and force her to recognize her unknown ability to transform into other people. The Sisters threaten the life of her brother Nate unless she marries a shadowy figure, the Magister, who wants to exploit her abilities. Tessa escapes with the help of Shadowhunters, demon killers, who try to keep order in the Downworld. The Shadowhunters are unsure of Tessa whether she is good or evil, but they must work together to stop the Magister before he takes over London and find Nate before it is too late. On this quest, Tessa is thrown into a dangerous underworld of vampires, warlocks, demons, and other supernatural folk. This is an action packed read that will leave readers breathless and clamoring for the next in the series. "Clockwork Angel" is the first in a series of prequels to the bestselling "Mortal Instruments" Series.