I am torn because I really liked this (and it may have been my favorite of the series, despite a drop in the number of delicious food descriptions) BUT as I think about it more, I really only liked the very satisfying last few pages.
The book follows two story lines: the first picks up a recurring thread from the previous books (Gamache's fight to winnow out corruption in the Surete) and this book's central mystery. Except, it never really felt like the central mystery -- it was some utterly bizarre murder that centered around a group of famous quints and it was half-heartedly tacked on. Indeed, at some points that investigation was used as subterfuge for doing further investigating into the corruption. Much was made about just how famous the quints were (world famous! The most recognizable girls in the world! EVER!) and maybe it's that I'm not Canadian or that I didn't grow up in that gentler, more innocent time, but I wasn't buying it. It didn't help that their identity was SO built up in advance and the reveal was...quints.
Anyway, so upon reflection, I don't think it worked very successfully. The main event was really the showdown between Inspector Gamache and basically everyone else in the Surete, so why have add on a weak and ridiculous quint murder mystery?
And this is dumb but I would use the word quintuplets to describe five identical people because quints reminds me of those creepy tiny baby dolls that were around when I grew up.