I had some really mixed feelings about whether this was a worthy or a warty read, but on balance, decided to rate it worthy. It's illustrated rather cartoonishly, but not badly, by Lauren Scheuer, and consists of twenty short mysteries, each just two or three pages long, combined together in a from which doesn't really have an overall story, but which ties the chapters together into one whole. The solution to each mystery can be found in the back, hidden under a lift-up door, rather like an advent calendar, so there's no chance of seeing the answer to the next mystery by accident.
The thing which made me feel that maybe this wasn't a worthy read was that the mysteries are for the most part rather simplistic, some ridiculously so, and many are also rather idiosyncratic: hinging on a misunderstood word, or on knowledge the reader is not explicitly given, but which they rather have to guess at. For example, one solution relied on the knowledge that the perp was left-handed, and nowhere in the story was this explicitly demonstrated, so the solution was only known for a fact to the girl who "solved" it. The reader simply had to guess at this answer, which is unsatisfactory. Some mysteries had more than one solution, unintentionally so, so they were a bit annoying.
On the other page, one or two of the mysteries were rather well done, and more than one made me consider kicking myself for not getting it, but then I'm really not very good at figuring these things out, which is why I like to read them. Plus, you never know where your next idea for a story will come from, and even this offers some food for thought if you're writing a detective story and need a muse to offer some ideas as to how to make this one scene work. It was for this purpose that I decided to rate this worthy: it makes the reader have to think, and in the case of middle-grade readers, that's never a bad thing. I don't plan on pursuing this series, but if you really like this one, there are at least two other volumes out there.