What I really loved about this book was the main character, Opal. She is not like most heroines that I've read about who always know exactly who they are and never falter. She is very human; plagued by doubts and never sure who she can trust, and never actually trusting herself. Unlike a lot of fictional characters, she is not a super-human. Opal has her times of weakness and tries her best not to be a coward, even though she thinks she is. Despite all of these things, she still remains strong enough to fight for those she loves, and begins to believe in herself. Set in the same world as Poison Study, Magic Study, and Fire Study. There are a lot of glassmaking terms and info, but it adds to the story instead of confusing it. Also what is interesting is her relationship with both Kade and Ulrick. I can't wait to read the next book.