As the 6th book in this series, you might think it would be a little too formulaic but that is not the case. A lot happens that makes it unique and it looks like it serves as a bridge - between the early books of the series which set the long term story arc up, and the final part which looks to deal with the series-long antagonist finally being dealt with.
It gives us some deep insight into the life of a character, Fred, who has been hanging around the main cast since the very beginning but until now was essentially an extra who would get called upon ti help out once in awhile. Having him take centre stage, and his particular nature, shifts away from the "couple comes together" formula we have seen until now. Simply put their isn't a romance in this one, just him and the other star of the book, Irina, focusing on saving Fred's brother. This time out the focus is the theme of family and looking out for your loved ones. Fred and Irina have a great friendship that develops over the course of the book and it was really fun to watch.
As alluded to earlier, we get a major reveal. Not only do we learn the identity of the Extra-magus that has been the series-long antagonist, but they are actually shown in person.
The other slightly different thing about this instalment was that other than a few five second appearances, the rest of the cast was not involved at all in helping Fred and Irina out - it was essentially all on the two of them, and it definitely allowed the to develop the friendship they did.
I'm more than halfway through the fun ride this series has been and it continues to be just as enjoyable, if not more so, than it has been since the beginning.