Glass 03 - Spy Glass - Maria V. Snyder

An undercover mission
leads to danger, adventure
and an impossible choice.
After siphoning her own blood magic in the showdown at Hubal, student glass magician Opal Cowan lost her powers. Immune to the effects of magic, Opal is now an outsider looking in, spying through the glass on those with the powers she once had. Powers that make a difference in the world.
Suddenly the beautiful pieces she makes begin to flash in the presence of magic and Opal learns that someone has stolen some of her blood. Finding it might let her regain her powers or discover that they're lost forever...