I highly recommend this book to teens who love suspense and fantasy.
Knight manages to successfully mix the demons Renata faces in her every day life-grief, regret, fear, jealousy-with the supernatural powers that she finds herself fighting. We see Renata emerging (literally and metaphorically) into her best self even as she moves backwards in time month by month watching her friends devolve and seeing their actions in the light of hindsight.
The author successfully hides the villain among a cast of suspects of equal measure and the ingenious revelation of the villain was a bit of a surprise yet plausible.
As I read I wondered how Renata would survive the events of the book emotionally even if she survived them physically. I cringed in anticipation of some sort of cop-out at the very end, but the author covered all bases and managed to end the book in a very satisfying manner.