During the first six books, the plot was predictable - Finding "someone" to get "something" for a single purpose.
However, when it comes to the final six books where the main trio needs to "return" said item. This is where the story can be unpredictable as you are now introduced to new characters that were not present in the first six books. These new characters and storylines were very interesting and fresh, quickly encapsulating my attention to understand what their next move was in each scenario. Some were funny but some were dangerous.
In the case of this book, The Nightwatchman is a proper villain with motives and pose a significant threat. The story is really good and you can actually see the main trio go around overcoming the challenge.
I would rate this one of the best books in the later series (I liked The Secret of the Changeling, Hunger of the Yeti and Flame of the Dragon the best).
Definitely worth reading!