Somewhere along the way my daughter heard about this book. Because a lot of the names were French, she was a little intimidated from reading it on her own, so I read it aloud to her.
Thanks to this book, I learned that "pamplemousse" is French for "grapefruit," and is used as a slang term for a breast. (The book itself didn't teach me any of this, but it gave me reason to do some Internet research, where these facts were awaiting my discovery.) A character is named M. Langoustine, which I learned a while ago from Wikipedia's "Rubio's Fresh Mexican Grill" page is a name for "lobster."
This book was a little weird because I felt Kingfisher was trying to pass off laziness as mystery. Are we supposed to think M. Langoustine is Mme. Pamplemousse's cat? That would be too hard to explain, but it would make the book more boring if it weren't true, so why not just hint at it and don't definitively say one way or the other? I'd be interested in what my daughter thought about this, but she's downstairs doing school right now, so I guess we'll never know.
Since no right-thinking author writes a one-off book these days, the true test of whether a book is any good is how interested a kid is in reading the rest of the series. By that measure, the Madame Pamplemousse books are very successful.
Rating: four and a half out of seven giant inflatable monkeys.