When we first meet Briar in the beginning of the quartet, he's a thief who has lived his life on the streets. Throughout the first three books he slowly changes, but we barely even notice it. Until this book.
In this book Briar is questioning who he is. He's come to the realization that he's not the person he used to be, and he's not sure who he is anymore.
In the midst of questioning who he is -- something that any preteen or teen should relate to, I think -- he finds his home under attack from a plague. One of his friends is the first victim of the plague, and he is afraid of his other friends also catching it.
Isn't one problem at a time enough? Does he have to deal with figuring out who he is and a plague at the same time? Then again, maybe how he handles the plague will help him discover the new person he is becoming.
This is a great book, and I recommend reading the quartet. I read the first book in it a few years ago but then didn't read any of the other books, which I now regret. They're so great that I wish I'd read them before. And trust me, the first two are great, but the last two books of the quartet are the best.