This is book number 1 in the Infernal Devices series.
“When 16-year-old Tessa Gray journeys from New York to London to join here brother, she is kidnapped and trapped in a fantastical world of werewolves, shape-changers and vampires. Tessa is rescued by the Shadowhunters, warriors dedicated to ridding the world of these demons. Tessa soon discovers who she might really be -- The Clockwork Angel -- and how she personifies the link between the Shadowhunters and demons in Victorian England.”
— Jack Blanchard, Fairy Godmother, Washington, DC