The Infernal Devices 1, Paperback Book, by Clare Cassandra

When sixteen-year-old Tessa Gray crosses the ocean to find her brother, her destination is England, the time is the reign of Queen Victoria, and something terrifying is waiting for her in London's Down world, where vampires, warlocks and other supernatural folk stalk the gaslight streets. Friendless and hunted, Tessa seeks refuge with the Shadow hunters, a band of warriors dedicated to ridding the world of demons. Drawn ever 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.