To start things off, out of the four books in this series I really honestly feel that the last one was the best. With the 3rd one being second best. It felt like the series was really coming into its own with the last two books, and especially this one. There was a lot more going on, you got to see it from numerous different perspectives and it was laid out very interestingly. The majority of the book takes place in the space of 7 days. And those 7 days were very interesting indeed. What I found the most interesting at the end, when it looks like everything was going to crap that the bad guys back in the Margolan capital had forgotten that their King who they were plotting against was a Summoner; or it just seemed that way. However, they were probably hoping that the ghosts did not want to hang around to tell their story or that Tris would be so angry and upset that he wouldn't listen. Either way, it was a very satisfying conclusion.
The loose ends were tied up, most of the good people came out a little beaten up. But it also ended with the idea that things are still not going to be good for awhile despite getting over this giant obstacle. It is very likely a lot of people in Margolan are going to go hungry, and potentially catch the plague that was started by the dark mages. Despite the war ending in Dark Haven, it is still quite possible that there will be some malcontents wanting revenge or to just stir up trouble. But at least the Flow is fixed, and not going to be exploding anywhere at any time. But this also leaves you wondering what is going to happen to the baby, and I personally was left really wanting to know more about Carina and Jonmarc's future twin daughters. I would have been so happy to have another series focused on them because they are honestly my favorite characters in the series.
Getting back to the 7 day layout, everything was moving really fast in those 7 days. It also really exemplified how much it sucks that they have to communicate by letter. So many things could have gone wrong with the timing being off. But I also felt like it was pretty realistic with what happened in the space of a day for each perspective being looked at. It kept the suspense up, because so many things were changing from day to day. It also really made you aware of how many things were going on simultaneously; which is sometimes difficult to get a sense of when you read some other books unless a certain event is specifically referenced between characters as a sort of orientation point. It also helped to keep everything neat and orderly so you wouldn't lose track of when something was happening; especially in the case of Carina and Jonmarc having things happen both during the day and at night, and on other days just at night.
Again, with the previous three books this book was a very fast read. And not because of it being short of substance. But it was honestly a good story going on, the suspense kept you going. This series is a very good one and I do recommend it to people when they are looking for a quick read. I have read the series more than once, not including re-reading it again for the sake of doing a review with the book fresh in my mind.