This is the fifth of five books telling the tale of Mags, an orphan made a mine slave and then Chosen as a Herald Trainee.
In my mind, it is the best of all the 'Collegium' books. It has a good story, it is fast moving (at least, compared to the other books!) and it introduces some new and very believeable characters, as well as answering a lot of outstanding questions from the earlier books. It is obviously set a long time earlier than Queen Selenay's rule, maybe not much more than 100 years afte the 'Last Herald Mage' which means that some aspects of Valdemar are different. The villages round The Bastion itself, for instance.
The one question I keep asking myself, though, is: 'Did Mercedes Lacky write this series?'. I'm still not sure. The style is totally different from most of her earlier books and if you compare Mags with Talia's pickpocket friend Skif (Take a Thief), there are considerable differences in the way the two similar stories are handled. Part of this may be due to a different publisher, Titan instead of Daw, with different sized books, different formatting and even different font styles, so that these books actually LOOK different, but to my mind, it doesn't read like she wrote them. Worked out the plot lines, yes, but the actual writing style doesn't seem to be hers - and this is maybe why some readers don't like the series.