I am looking for a book where the sorcerers bond with special stones to use their magic, and the main character unknowingly steals a sorcerer's stone, almost dies from the stones power, and is saved and made that sorcerer's apprentice? The main character is a street boy, and the sorcerer teaches him to turn into a black cat, I think. He eventually breaks into the Palace and tries to steal the queen's necklace, because it is his stone. The sorcerer is disgraced and lives in a half-destroyed castle.
I remember that when the main character was pick-pocketing the sorcerer, he says something like "If he can pay to be snooty, he can pay for my lunch." (not exact).
I can't remember any more than that, and the book seems to be from several years ago, in the early 2000's.