Piper is the second book in the Jerrick series.
In the first book, Michael has been spirited away / rescued from the Grand Inquisitors to their enemy The Council. It’s not clear which side is good and which is evil as neither are either.
We get a bit more about fairy tale history in this book, with Grimm being a librarian and what legend says is The Pied Piper of Hamlyn being the Piper of the title.
This is quite a long book and gets exciting in parts. There’s also some rather nasty characters and death is always on the outskirts. I found this to be a well-rounded story with some great characters.