Ahoy there me mateys!  I say this every time I finish one of these novellas but I seriously could read dozens of books set in the various worlds.  This is the first book in the series to take place on Earth and will make little sense to someone not familiar with the series (number 3 and 6 are required prerequisites).  In this installment, Cora is the focus.  Her time in the previous books has not been kind to her mental state and she is desperate.  So much so that she transfers to another school called Whitethorn whose approach to doorways is different.  Only Cora is horrified by the methods used and has to figure out what to do next.  While this book expanded the worldbuilding and understanding about doorways, it also it some ways felt like a bridge book opening up a larger conflict to come.  I want more!  Arrrr!