Shatterglass - Tamora Pierce This is the last in the Circle Opens series which in itself is a spin off of the Circle of Magic series. In the Circle of Magic series, 4 people - Tris, Briar, Daja and Sandry are found to have magical abilities and taken to a school for learning. In the Circle Opens series, each of the four is out in the world and comes across a magical child who needs to be mentored. I enjoyed each of the 8 books but I think this one is my favorite.

One of the rules of becoming a Mage is that if you find a magically gifted person without a mentor, you must find one for them or if all else fails, become their mentor. Fourteen year old Tris Chandler is a mage and during her travels comes across Kethlum Warder, a man with mage-like abilities but with no training or mentor. According to the rules, Tris must now become his mentor. Reluctantly she does and while teaching him lightning magic, they get involved in the murder investigation of a bunch of murdered lower class women. Excellent! An interesting mystery along with a magical journey through the wonders of glass-blowing.