It is my.opinion that these stories should be read in order. AN UNEXPECTED SEQUEL is the 4th book in the series and there are threads and characters rom the previous stories.
Each book in the series is a short, quick read and while the first three felt light and whimsical, this story was just a little bit darker. I think we are being given hints of what is to come.
This almost like chapter books for adults and as such has held my attention throughout.
Review by @mauraharper