Adventures on Trains has fast become one of my favourite middle grade series, and it was lovely to see Hal solve another mystery. The book was quite atmospheric especially towards the end. 

While I enjoyed it though, it was a rare case of a 4 star read being a bit disappointing - I've given all the previous books in the series 4.5 stars or higher. It took much longer for me to be gripped by the story than with the other three books. At times it felt like it was trying to be more of a spy story than a cosy mystery, which didn't quite work for me, and I also wanted more of the story to actually take place on a train. 

A good book, just not quite what I'm looking for from this series.