This is the fourth book in R.L. LaFevers' Theodosia Throckmorton series and currently the last in the series, though there is some indication that a fifth book may be on the horizon. These books rely heavily on each other and should be read in the order in which they were published.
This book takes the series to somewhat of a closure but simultaneously opens several new lines of questions that will hopefully bring about several additional books or possibly prequels.
It is a well-written series that deserves more attention from the author.