The main plot being related to Heinrich Kramer, the writer of The Malleus Maleficarum (Hammer of Witches') was a little odd since I have heard of Kramer and Malleus Maleficarum (although I had more sense than Cat and didn't try to read it!). I know Vlad is in this series, but he's often used in various paranormal series since he's "Dracula" but it was still a bit of a shock.
This plot is mainly focused on ghosts. It was different from the other books in that way, since most of them have been focused on vampires or humans. It was nice to learn more about the ghosts in this series, since they are often in the background (since all (?) vampires in this series can see ghosts)
I was sad that Vlad wasn't in this one but the next book is his book (really part of the Night Prince series, but I'm going by the publication order and not just the Night Huntress series order).