Briar's book is the last of the Circle of Magic quartet. A new and mysterious illness, not to mention deadly, breaks out in Summersea. As it spreads, and more and more succumb to the disease, Tris, Daja, Briar, and Sandry aid their teachers in combating the epidemic. The entirity of Winding Circle does all it can to find a cure and fight back before the illness overtakes them all. 
 This is my favourite of this quartet. The plot of the novel is fairly simple, without the need for complex turns and suspense to keep the reader enthralled. The story progresses at a believable pace, and the twists that Pierce does insert are wonderful. 
 Like the previous Circle books one of the four children is focused on (Briar, in this case) while still giving some POV from the others. With the passage of time between the earlier books one can see how the children, and the adults, have grown. All of the characters feel fleshed out, even Dedicate Crane who was fairly dismissed earlier in the series. 
 As always, Pierce's writing is lovely. The descriptions of the use of magic vary from the way it's described in the Tortall books. I perfer the Emelan's description of magic better, having more of a practical than mystical feel. Also, this book feels very well researched in reference to the epidemic and epidemic procedures, which always makes me happy. All in all? Wonderful.