Book excerpt: A prequel to Cassandra Clare's Mortal Instruments series, The Infernal Devices is the story of Tessa Gray, a sixteen-year-old American girl traveling alone to Victorian London who runs afoul of the city's sordid supernatural underworld. Rescued by the Shadowhunters of the London Institute, Tessa quickly finds herself caught up in an intrigue that may very well destroy her new friends - including the two enigmatic young men, Jem and Will, who have taken her under their wing...