The Lost Book of the White (Broché)

Life is good for Magnus Bane and Alec Lightwood. That is, until the night that two old acquaintances break into Magnus's apartment and steal the powerful Book of the White. Now Magnus and Alec will have to drop everything to follow the thieves to Shanghai. And Magnus has been stabbed with a strange magical weapon that is changing the very nature of his powers. Fortunately, they have backup in the form of Clary, Jace, Isabelle and Simon.
In Shanghai, they learn that a much darker threat awaits them. Magnus's magic is growing unstable, and if they can't stop the demons flooding into the city, they might have to follow them all the way back to the source — to the very realm of the dead.