When sixteen-year-old Tessa Gray arrives in England during the reign of Queen Victoria, something terrifying is waiting for her in London's Downworld, where vampires, warlocks and other supernatural folk stalk the gaslit streets. Friendless and hunted, Tessa weeks refuge with the Shadowhunters, a band of warriors dedicated to ridding the world of demons. Drawn even deeper into their world, she finds herself fascinated by - and torn between - two best friends and quickly realizes that love may be the most dangerous magic of all.