I always enjoy Julie Hyzy's mysteries; as a writer, she doesn't burn a series out with a spectacular book or two, with mediocrity dragging the remaining books down. Her writing, character development and plotting are even and steady and her series' arcs are a slow burn, rather than a flash in the pan.
Grace to the Finish was actually slightly less about the murder mystery (although that was good too), than it was the resolution to a series long arc concerning her sister. Hyzy's solution was clever, if a little bit convenient. The actual mystery was ok, but less a puzzle for the reader to solve than the narrative of the mystery's solution.
With cozy series one can never be sure if the titles aren't a indication of the series' status, so Grace to the Finish could very well be the last book; if so, it ends in a pretty good place without a lot of loose threads left dangling. But if there's a ninth book, I look forward to it with pleasure.
Book themes for Las Posadas: Read a book dealing with visits by family or friends, or set in Mexico - Grace has to deal with her sister's return and a visit from her long absent Aunt. These two are major players in the plot.