This volunme is more of a tangent to the main story at the heart of the other three books in the series, however, completists will want to read it so find out what happens to Strat's sister Devonny. Annie's brother Tod and Devonny are okay protagonists, but I found that I missed the main characters of the other books.
This is one of the best series I've read. I love all of them. This one is more focused on Devonny as opposed to Strat as the rest of the books are. I would suggest this to about anyone!