I really enjoyed this book and it is a book that is on a higher maturity level than the original Circle of Magic books. Among the themes at play here are Sandry's devotion to her uncle and her desire to care for him out of selfless love as opposed to the selfishness of Duke Vestry's third son and current heir. In the original Circle of Magic books we saw Sandry as both the most psychologically damaged of the four youths due to her accidental imprisonment in the dark and also as the most compassionate of the four (think of how the children came to adopt the dog, Little Bear). During the Blue Pox she worked herself to the bone to provide the medical gear that the Water Temple forgot about. Also, she was the one that wove the four friends' magic together, then tirelessly sifted them apart again.
Sandry's caring/motherly instincts extend to the young boy she comes across during an outing with her uncle. Like Sandry herself was, he is an unrecognized magical talent, with his specialty being dance magic. As becomes the theme in Street Magic as well, Sandry finds herself having to mentor this youth while uncertain of her ability and skill to do so. Yet, with the help of her mentor, Lark, she manages to persevere. The underlying theme here as well is that the boy's family at first is not that thrilled that he is a mage who is aspected to dance magic. The family serves the local guard and to be a mage in the family means a university education at Lightsbridge, with strictures and set expectations. Winding Circle magic the opposite as the methodology is to find that which is particular to the individual, not to bend the individual to the strictures.
Of course, to make things juicy, Ms. Pierce needs something to be going on that keeps us exciting, reading and on the edge of our seats. More so than in Street Magic, the antagonists of this book provide murder, mystery and mayhem. While we feel little sympathy at first for the murder victims, it is the continuing targeted assassinations that we are concerned with and the widening circle of people at danger. The assassins are using magic that confounds both the duke's men and Sandry until they finally start to piece things together. What makes it all worse for everyone involved is the concept of addiction and decay inherit in the dangerous methodologies of the assassins.
As I said before, this is a more mature book than the previous Circle of Magic books as we are introduced to outright blood, murder and many of the dark sides of human nature. Ms. Pierce does a better job with the murder/mystery plot in this book than she does in some of the other Circle of Magic stories.
While the Pebble Sea setting is very much a highly evolved Renaissance one (Ms. Pierce based much of the world on the Mediterranean), there seemed to be a few things that were a bit too modern for me, but that is mostly my nitpicking. I did have a few issues with the dance studio that was introduced, though its instructor was a highly engaging character. The studio just seemed a bit too modern for me.
Overall, I highly recommend this book and its companions for young readers. Despite the bloody and dark aspects that you will find throughout, I feel that the underlying themes are extremely positive and good.