Showing The Magic Thief by Sarah Prineas

Conn, the gutterboy thief who became a boy magician, has been made Magister of the city of Wellmet. But before long, he is back in trouble.

Conn and his little dragon Pip are accused of stealing other magicians' locus stones, the source of their power. Conn must go back to his life as a ragged gutterboy and slip into the dark and dangerous Twilight part of the city to discover the real thief and save Wellmet from a dark evil...