Blade Singer by Aaron De Orive

Manny Boreaux, a troubled adolescent from Texas, is magically transported into the body of a goblin pickpocket in an alternate world inhabited by faerie creatures. Manny must quickly adapt to the danger all around him and try to find a way to get back home, a feat complicated by the pickpocket's association with a notorious gang of thieves. But when Manny uncovers a plot to assassinate a young king, he must enlist the aid of an elf cavalier and a cat burglar to thwart a Sidhe witch's scheme to ignite a civil war between humans and the Fae.